- fixed typo in USDF spec.
- comment fixes taken from GZDoom.
- division by zero check in R_SetVisibility from GZDoom.
- d_dehackedactions no longer exists.
- updated .gitignore to ignore all compile generated files.
- added Edward-san's patch for allowing 'clang' compiler to use the same 'gcc' cmake settings
- added _mental_*s compatibility fix for Ultimate Simplicity, map07
- added DavidPH's patch for compiling with FModEx 4.44.01.
- DavidPH's patch for Linux compilation.