PartialField Descriptor

Can build query for partial field (first attempt)
Test for PartialFields query.
Test for many partial_field queries.
Partial Fields Response

Partial fields response building based on reflection library and custom
dictionary like class
Refactoring part 1.
Move MyDictionary to separate file. Minor refactoring.
Renaming.
PartialFields integration test.
Merge branch 'master' of github.com:loled1728/NEST into partial-field-support