create archive directory if it doesn't exist
fix update.rss timestamp generation

makes sure that if we have a version that is not a timestamp, then we
can still build the rss feed. this is a terrible hack and probably needs fixing.
Enable stable package building for git.

Builds in the plumbing for checking out stable versions of git/github packages.

Contributions by @Bruce-Connor and @Wilfred.
Add stable package building Makefile and services
update the readme for stable packages