CI test the Ceylon website build

[crawley]

My recent problems with building the Ceylon website suggest that it would be a good idea to add a test to your CI server to do a fresh checkout and build of the site into a fresh RVM instance. At least, get to the point of running "awestruct -d" and checking that it doesn't bail out immediately. (Or equivalent.)

That way, you will discover sooner about build problems caused by upstream changes to the gems that the website depends on.