function_score unit/integration tests

[Mpdreamz]

@andreabalducci was kind enough to pretty much implement all of the new function_score query stuff #387

Still needs some unittests and integration tests before we can release it.

See also #370

[andreabalducci]

I can find some slots for os dev next week, If you want I can take care of the integration tests.

[jimsorock]

@andreabalducci @Mpdreamz thank you for this update. I was wondering if this includes being able to apply filters to the functions. thanks

[Mpdreamz]

PR #451 implemented filters :)