Tracing debugger, expressions, thread states, and pretty formatting

This is a two part update.

A Jython debugger. This is a complete reimplementation of the built in Python Debugger, but upgraded, fixed, and revamped to take advantage of the more sophisticated class objects of Python 2.4+ as well as the multithreaded environment of Java. It's a massive, complicated beast with lots more documentation and details to follow later.

The metatools see an update to the pretty printer, with much more extensive formatting methods and the ability to take over the interactive prompt's replies via shared.tools.pretty.install() - simply call that and all objects that would otherwise get printed via repr now get the better formatting.
Dataset filtering and threads have more extensive tooling.
Expressions have been added to support the debugger's trap creation. These are halfway to compiled, and can be directly inspected, unlike compiled code.

NOTE: Debugger build artifacts are based on commit a2b358c