PurrFX project update 13

Project status overview as of September 1, 2020.

Commits: August 31 through September 1, 2020.

The latest library update is aimed at improving cross-platform compilability. For example, when using the library on Windows, so-called wide chars (wchar_t) are used for file paths. Also, I've tried compiling and running a test project on linux with the g++ 9 compiler. Based on this experience, the library was modified accordingly.

Project page: https://github.com/TheCatNose/PurrFX