Partial implementation of the top hits aggregation

TODO: Still need to implement a top hits response object and handle
deserialization in the AggregationConverter class.
Merge branch 'feature/aggregations-top-hits' of github.com:elasticsearch/elasticsearch-net into feature/aggregations-top-hits

Conflicts:
	src/Nest/DSL/Aggregations/AggregationDescriptor.cs
	src/Nest/Nest.csproj
	src/Tests/Nest.Tests.Integration/Aggregations/MetricAggregationTests.cs
added support for Top Hits aggregation
A tad of aggregation documentation
Markdown didn't like <> outside code tags...
Merge pull request #942 from andersosthus/documentation

AggregationContainer documentation
Fix #934 Exposed DoRequest on NEST and Elasticsearch.NET clients
 added tests to debug #945 ignored for now but once tests are refactored so we can start nodes in desired states they should become relevant again
when not using connection pooling and an exception occurs in the IConnection layer do not retry and bubble out immediatly, the chances of the call succeeding a second time are slim
fix #947 add support for compressed responses and basic auth on the alternative http connection
Merge branch 'develop' into feature/aggregations-top-hits
made Score backward compatible
added a test trying to capture #931 unsuccesful but the test is still good to have around
fix #931 Percentiles aggregation parser did not fully read the json to completion causing adjecent buckets not to be properly parsed as well
Merge pull request #940 from elasticsearch/feature/aggregations-top-hits

Feature/aggregations top hits
Fix CatShards tests

Previously asserting that Node or Docs were not null or empty, but this
isn't a valid test when unassigned shards exist in the cluster.  In this
case, the cat api will return an empty string.  Switched to test for state
which should always be present.
Fix FieldsTest: should not search all types

The Content field is being checked for, but only the elasticsearchprojects
type contains this field.  This was causing an ArgumentNullException.
Decouple ScrollTests from number of shards and docs
Skip GeoBounds agg test on ES versions <= 1.3
Skip percentile ranks and top hits tests on ES < 1.3