renamed a bunch of enums to follow c# conventions
added string enum converter
Merge branch 'feature/normalize-enums' of github.com:elasticsearch/elasticsearch-net into feature/normalize-enums

Conflicts:
	src/Nest/Domain/Mapping/Attributes/ElasticPropertyAttribute.cs
	src/Nest/Nest.csproj
fixed post merge build errors
added StringEnumConverters to the remaining enums
Replaced all the Enum.GetNames to extension method taking into account EnumMember, fix #739 fix #740