Added std::string variants of DsonObject functions.

These require a conversion from std::string to std::wstring internally.
Also made the operator[] in DsonObject/DsonArray work.
Also added "inline" for getters/setters in DsonObject/DsonArray.
fixup! Added std::string variants of DsonObject functions.

These require a conversion from std::string to std::wstring internally.
Also made the operator[] in DsonObject/DsonArray work.
Also added "inline" for getters/setters in DsonObject/DsonArray.