Added filesystem::make_relative

I'll need to update all include and linker paths from the temp directory
in which I'm compiling to the source directory. It sucks, but I see no
way in clang to change the working directory and compiling files
in-source leaves the potential for abandoned temp files.
Added absolute pathing for cmdline args

This allows me to build the sources in a temp directory, likely to be
/tmp/color_coded while keeping header search paths working properly.
Merge branch 'master' of github.com:jeaye/color_coded into readme