add various cmake outputs to .gitignore
remove broken Makefile
CMakeLists.txt: remove stdc_test.c after we're done with it
implement texture_font_new_from_*() functions

this commit renames texture_font_new() to texture_font_new_from_file()
and also implements texture_font_new_from_memory() for creating
texture fonts from font files that are already loaded somewhere in
memory (for example, fonts embedded inside an application).