Errors compiling with Windows as-is

[ntjess]

As is, compiling on MSVC2017 produces an error since wcsncasecmp and some other terms are undefined. This is because #if defined(WIN32) && !defined(GNUC) [line 32 in json.h] should use _WIN32 instead (note the underscore as the first character).

This manifests itself elsewhere in the project too (e.g. JSON.cpp line 52)