[BUG] Cpprestsdk - ModelBase.cpp fails to compile on Kubuntu 14

Created by: TomerJLevy

Hi,

The sample of cpp-restsdk/client/ModelBase.cpp fails to compile on Linux. The same Cpprestsdk version compiled fine using v4.0.2 generator.

Because of line 299:

"No matching function for call to 'utility::datetime::from_string(const wchar_t....).." "Candindate is: utility::datetime::from_string(const string_t....).."

In which 'string_t' is defined in 'cpprestsdk/Release/include/cpprest/details/basic_types.h' as std::wstring for Windows or std::string for POSIX: link here: https://github.com/microsoft/cpprestsdk/blob/master/Release/include/cpprest/details/basic_types.h#L52

For me, removing the 'U' before the "NULL" does the trick but it's not a bug fix.