Aggressive compressions in the encoding.

* Give very short names to classes used very often
  (Object, String, Functions, Tuples, primitives)
* Compress package prefixes used very often
  (scala.collection, java.lang, etc.)
* Use 1-character names for env top-level fields and
  array underlying.
Merge pull request #535 from sjrd/shorten-sigs

Aggressive compressions in the encoding.