Add function for checking wether file exists to osinterface, BMP screenshots can now be saved without WIN32 specific methods.
replaced WIN32 file i/o in config_load()
replaced WIN32 file i/o in config_save()
clean up header files, keep windows.h for MAX_PATH
travis doesn't like capitalized <Windows.h> ...
Merge branch 'os-specific' of https://github.com/atmaxinger/OpenRCT2 into atmaxinger-os-specific
Merge branch 'atmaxinger-os-specific'