added FunctionScoreQuery
added FuncionScoreQuery (gauss & boost_factor)
renamed FunctionScoreMode
Renamed FunctionScoreScoreMode in FunctionScoreMode
Merge branch 'function_score' of github.com:andreabalducci/NEST

Conflicts:
	src/Nest.Tests.Unit/Nest.Tests.Unit.csproj
	src/Nest/DSL/Query.cs
	src/Nest/DSL/QueryDescriptor.cs
	src/Nest/Nest.csproj
post merge touchups of the function_score PR #387