Port to Ceylon

Implements #1.

The project layout has changed a bit with this; most notably, the ANTLR runtime is no longer contained in the repository, but instead expected as a dependency of the Ceylon typechecker; the necessary modifications to the IDE's defaultRepository are outlined in README.md.
Minor improvements

* Remove unneeded imports
* Ignore modules/ and classes/
* Speed up formatting marginally (hopefully) by means of a faster way to
trim the indentation string
* Remove unnecessary string optimizations in testSamples