Move release tarballs from chad's freedesktop home dir to github

Change the url for each file "waffle-${version}.tar.xz".

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
Move all release artifacts to github release pages

Remove the directory 'files/releases', which contained all non-tarball
release artifacts. For example, for waffle-1.3.0 the non-tarball release
artifacts were:

    waffle-1.3.0-announcement.txt
    waffle-1.3.0.sha256sums
    waffle-1.3.0.tar.xz.sig

Relocate the non-tarball artifacts to the same location as the tarballs,
which were recently relocated to the Github release download pages
[https://github.com/waffle-gl/waffle/releases/download].

Update the urls in release.html.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>