Release Snappy 1.1.3; getting the new Uncompress variant in a release…

… is nice,

and it's also good to finally get an official release out after the migration
to GitHub.

The GitHub releases are basically done by tagging a commit and then uploading
the .tar.gz file generated by make dist as a binary asset; GitHub will add
all files on the tagged commit on top of the tarball and recompress, but since
we don't have any nodist_* files in configure.ac, this works fine for us.
(As far as I can see, this behavior of GitHub--uncompressing the .tar.gz,
and the behavior of silently ignoring files in it that are also in the git
repository--is undocumented, but also seems to be used in some official
screenshots, so I guess we can rely on it.)

A=sesse
R=jeff