Added API for writeconcern objects. This API is very desireable with working with host programs written in another languages to avoid having to declare and maintain the structs in other language (ex. Delphi) Writeconcern objects are created, destroyed and manipulated using API instead of accesing fields directly
Added specific tests to check every API function to make sure they set values right and get values right
Added a warning message about the values set to write_concern on tests. They don't align with possible values or meaninful values but rather test scenarios to verify there's no crossover between attribute setting and getting
Merge pull request #121 from jsbattig/mongo-pull-request-writeconcern-api

Added API for writeconcern objects