gitignore: Start tracking zip files

Stop ignoring *.bz2 *.gz *.xz *.zip
release: Import all release artifacts

I want all release files to have long-lived, near permanent urls. I do
not want urls for release artifacts to become stale when Waffle moves to
a new hosting provider (currently Github).

Therefore, the urls cannot refer to github.com. A simple solution: for
each release artifact, make its url *relative*.

- Import tarballs, checksums, gpg signatures, release notes, and
  announcement emails.
- For each release artifact, change its url to
  "files/release/${waffle_tag}/${filename}".

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
video: Move XDC 2012 presentation files to archive.waffle-gl.org
video: Use HTML5 <video>, not YoutTube, for XDC2012 talk
video: Add mp4 alternative for Apple users

Safari does not support webm.