The site was generated, but updating the gh-pages branch was included
in the `publishSite` target. So a new target is added and called,
`updateSite`.

The major change is switching from `publishBinaries`, which still
exists and uploads to Bintray, to `releaseBinaries`, which creates
a draft release on GitHub and uploads the binaries.

Another change is some reordering. Now first the binaries are
uploaded, the maven artifacts pubished and the tag and site pages
pushed. Then the GitHub release is made public.
Only after that is the minor version bumped and pushed.

The whole script could use some error checking and stoping when
things go wrong, instead of blindly continuing.

A minor change, and temporary, is that we need and check for Ant 1.9,
as we still build with Java 7.