first cut at QuakeLive pk3 support

Using the XOR data from Luigi Auriemma.

Built via "nmake NEW_COMPILER=1 MY_STATIC_LINK=1" from the CPP\7zip folder.

Only tested briefly in FileManager so far. It seems to correctly open
QuakeLive pk3s (as well as "normal" pk3s) and be able to create QL pk3s. At
least they correctly translate back and forth using quakelivedec.

todo:
- more testing of the output, including actually running a pk3 using QL
- investigating/testing the results from non-FileManager make targets
- more code commenting
- readme for the repository
- possibly edits to the files under the DOC directory
- integration with FileManager context menu
- possibly integration with Explorer context menu
- possibly updating appropriate .dsp files
- thinking about / experimenting with different write-staging buffer sizes
- seeing if some Zip options result in invalid pk3s
- moving todo list into GitHUb issues!