Added new examples (#1031)

* Added new examples

* Fixed examples links

docs/examples/reindex.asciidoc

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+[[reindex_examples]]
+== Reindex
+
+The `reindex` API extracts the document source from the source index and indexes the documents into the destination index. You can copy all documents to the destination index, reindex a subset of the documents or update the source before to reindex it.
+
+In the following example we have a `game-of-thrones` index which contains different quotes of various characters, we want to create a new index only for the house Stark and remove the `house` field from the document source.
+
+[source,js]
+----
+'use strict'
+
+const { Client } = require('@elastic/elasticsearch')
+const client = new Client({ node: 'http://localhost:9200' })
+
+async function run () {
+  await client.index({
+    index: 'game-of-thrones',
+    body: {
+      character: 'Ned Stark',
+      quote: 'Winter is coming.',
+      house: 'stark'
+    }
+  })
+
+  await client.index({
+    index: 'game-of-thrones',
+    body: {
+      character: 'Arya Stark',
+      quote: 'A girl is Arya Stark of Winterfell. And I\'m going home.',
+      house: 'stark'
+    }
+  })
+
+  await client.index({
+    index: 'game-of-thrones',
+    refresh: true,
+    body: {
+      character: 'Tyrion Lannister',
+      quote: 'A Lannister always pays his debts.',
+      house: 'lannister'
+    }
+  })
+
+  await client.reindex({
+    waitForCompletion: true,
+    refresh: true,
+    body: {
+      source: {
+        index: 'game-of-thrones',
+        query: {
+          match: { character: 'stark' }
+        }
+      },
+      dest: {
+        index: 'stark-index'
+      },
+      script: {
+        lang: 'painless',
+        source: 'ctx._source.remove("house")'
+      }
+    }
+  })
+
+  const { body } = await client.search({
+    index: 'stark-index',
+    body: {
+      query: { match_all: {} }
+    }
+  })
+
+  console.log(body.hits.hits)
+}
+
+run().catch(console.log)
+----

docs/examples/sql.asciidoc

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+[[sql_examples]]
+== SQL
+
+Elasticsearch SQL is an X-Pack component that allows SQL-like queries to be executed in real-time against Elasticsearch. Whether using the REST interface, command-line or JDBC, any client can use SQL to search and aggregate data natively inside Elasticsearch. One can think of Elasticsearch SQL as a translator, one that understands both SQL and Elasticsearch and makes it easy to read and process data in real-time, at scale by leveraging Elasticsearch capabilities.
+
+In the following example we will search all the documents that has the field `house` equals to `stark`, log the result with the tabular view and then manipulate the result to obtain an object easy to navigate. 
+
+[source,js]
+----
+'use strict'
+
+const { Client } = require('@elastic/elasticsearch')
+const client = new Client({ node: 'http://localhost:9200' })
+
+async function run () {
+  await client.index({
+    index: 'game-of-thrones',
+    body: {
+      character: 'Ned Stark',
+      quote: 'Winter is coming.',
+      house: 'stark'
+    }
+  })
+
+  await client.index({
+    index: 'game-of-thrones',
+    body: {
+      character: 'Arya Stark',
+      quote: 'A girl is Arya Stark of Winterfell. And I\'m going home.',
+      house: 'stark'
+    }
+  })
+
+  await client.index({
+    index: 'game-of-thrones',
+    refresh: true,
+    body: {
+      character: 'Tyrion Lannister',
+      quote: 'A Lannister always pays his debts.',
+      house: 'lannister'
+    }
+  })
+
+  const { body } = await client.sql.query({
+    body: {
+      query: "SELECT * FROM \"game-of-thrones\" WHERE house='stark'"
+    }
+  })
+
+  console.log(body)
+
+  const data = body.rows.map(row => {
+    const obj = {}
+    for (var i = 0; i < row.length; i++) {
+      obj[body.columns[i].name] = row[i]
+    }
+    return obj
+  })
+
+  console.log(data)
+}
+
+run().catch(console.log)
+----

docs/examples/update-by-query.asciidoc

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+[[update_by_query_examples]]
+== Update By Query
+
+The simplest usage of _update_by_query just performs an update on every document in the index without changing the source. This is useful to pick up a new property or some other online mapping change.
+
+[source,js]
+---------
+'use strict'
+
+const { Client } = require('@elastic/elasticsearch')
+const client = new Client({ node: 'http://localhost:9200' })
+
+async function run () {
+  await client.index({
+    index: 'game-of-thrones',
+    body: {
+      character: 'Ned Stark',
+      quote: 'Winter is coming.'
+    }
+  })
+
+  await client.index({
+    index: 'game-of-thrones',
+    refresh: true,
+    body: {
+      character: 'Arya Stark',
+      quote: 'A girl is Arya Stark of Winterfell. And I\'m going home.'
+    }
+  })
+
+  await client.updateByQuery({
+    index: 'game-of-thrones',
+    refresh: true,
+    body: {
+      script: {
+        lang: 'painless',
+        source: 'ctx._source["house"] = "stark"'
+      },
+      query: {
+        match: {
+          character: 'stark'
+        }
+      }
+    }
+  })
+
+  const { body } = await client.search({
+    index: 'game-of-thrones',
+    body: {
+      query: { match_all: {} }
+    }
+  })
+
+  console.log(body.hits.hits)
+}
+
+run().catch(console.log)
+
+---------

docs/examples/update.asciidoc

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+[[update_examples]]
+== Update
+
+The update API allows updates of a specific document using the given script. +
+In the following example, we will index a document that also tracks how many times a character has said the given quote, and then we will update the `times` field.
+
+[source,js]
+---------
+'use strict'
+
+const { Client } = require('@elastic/elasticsearch')
+const client = new Client({ node: 'http://localhost:9200' })
+
+async function run () {
+  await client.index({
+    index: 'game-of-thrones',
+    id: '1',
+    body: {
+      character: 'Ned Stark',
+      quote: 'Winter is coming.',
+      times: 0
+    }
+  })
+
+  await client.update({
+    index: 'game-of-thrones',
+    id: '1',
+    body: {
+      script: {
+        lang: 'painless',
+        source: 'ctx._source.times++'
+        // you can also use parameters
+        // source: 'ctx._source.times += params.count',
+        // params: { count: 1 }
+      }
+    }
+  })
+
+  const { body } = await client.get({
+    index: 'game-of-thrones',
+    id: '1'
+  })
+
+  console.log(body)
+}
+
+run().catch(console.log)
+
+---------
+
+With the update API, you can also run a partial update of a document.
+
+[source,js]
+---------
+'use strict'
+
+const { Client } = require('@elastic/elasticsearch')
+const client = new Client({ node: 'http://localhost:9200' })
+
+async function run () {
+  await client.index({
+    index: 'game-of-thrones',
+    id: '1',
+    body: {
+      character: 'Ned Stark',
+      quote: 'Winter is coming.',
+      isAlive: true
+    }
+  })
+
+  await client.update({
+    index: 'game-of-thrones',
+    id: '1',
+    body: {
+      doc: {
+        isAlive: false
+      }
+    }
+  })
+
+  const { body } = await client.get({
+    index: 'game-of-thrones',
+    id: '1'
+  })
+
+  console.log(body)
+}
+
+run().catch(console.log)
+
+
+---------