Extract the gas2masm project

Remove the directories 'WinQuake/gas2masm', and 'QW/gas2masm' and place
the important source, and build files into a separate Git repository.
This repository is included via a Git sub-module.

All __Windows__ versions of Quake require the gas2masm project to
convert files that can be interpreted by the _GNU_ Assembler into files
that can be understood by the _Microsoft Macro_ Assembler. However, the
source code released includes two copies of this project. If changes are
made, this could lead to differences; in turn leading to errors.