Archiver script improvements.

Relating to #235.

* Rolled back to using deflate for zip files, as some Windows versions
don't support LZMA, which could confuse users into thinking the archive
is broken.
* Added support for using 7-zip if it is installed.
* Added archive filename versioning using `git describe --tags --long`
if git.exe is found in the PATH or in a GitHub for Windows install.