First stab at builtin set_color. Moved set_color.cpp to builtin_set_color.cpp and taught fish about it.
Remove set_color from Makefile. Fix issue where builtin_set_color would mix output modes up
bulitin_set_color.cpp -> builtin_set_color.cpp
Remove set_color.cpp from Xcode project
Teach set_color to call setupterm so it doesn't crash when run non-interactively
Teach fish how to clean up installed versions of set_color