TextConv: Added C++ string/wstring wrapper functions.
dllmain.cpp: Don't use "using namespace std;".

Explicitly specify which classes from std:: we should import.
IniFile: Added WString accessors.

The INI data is stored using UTF-8 internally. The WString accessors
make it easier to convert the UTF-8 text to UTF-16 for use with
Win32 Unicode functions.
dllmain.cpp: Use Unicode filenames where possible.

TODO: Update FileMap to use Unicode filenames as values while still
keeping ANSI filenames as keys.
dllmain.cpp::InitMods(): Get both the path and filename of sonic.exe.

TODO: SetDllDirectory() is only available if _WIN32_WINNT >= 0x0502.
Either call it using GetProcAddress(), or increase _WIN32_WINNT to 0x0502.