Start hacking on the code to make it more embeddable as a library.

This splits bits of functionality in tester.main() out into separate
entry points so that a client python module could call into typ to
do stuff.
- export STATUS_FORMAT for a default
- expose the default_job_count()
- expose a run() method separate from main()
- expose trap_stdio() and release_stdio() to override the system streams
  so that callers can control this if need be.

This is a long way from right, but it's a start.