Minor refactor for mingw, data type tweaks, and warning removal.

[SolomonSklash]

I made a few minor tweaks to better support mingw and to reduce compiler warnings:

• Added function signatures to corresponding header files to remove no previous declaration for warnings.
• A new header darkmodule.h was created to contain the _DARKMODULE struct definition. This is so that darkloadlibrary.h can include each of the other headers with their new function signatures.
• A couple variables were PCHARs instead of PWCHARs.