Unify auth handling in the Host class

- flatten auth config to an Authorization header when the Host is created
 - remove individual Authorization handling from connectors
 - removed incomplete support for per-request auth
 - use per-request headers to provide your own Authorization header per request

test/unit/browser_builds/generic.js

@@ -6,9 +6,11 @@ describe('elasticsearch namespace', function () {
   it('is defined on the window', function () {
     expect(es).to.be.ok();
   });
+
   it('has Client, ConnectionPool, Transport, and errors keys', function () {
     expect(es).to.have.keys('Client', 'ConnectionPool', 'Transport', 'errors');
   });
+
   it('can create a client', function () {
     var client = new es.Client({ hosts: null });
     expect(client).to.have.keys('transport');