Add a simple and fast test runner

* Only needs to be compiled once and can directly run tests files.
* A list of either dumped functor (.ozf) or test files (.oz) can
  be given and they are evaluated directly.
* .oz files are compiled in memory and avoid the cost to pickle
  and dump/load from disk, which is very practical when editing
  a test (the normal runner needs that .oz compiled, then run the
  runner to produce oztest, which can executed in a 3rd execution).
* Very minimal, so does probably not support all tests, yet all of
  platform-test/base/*.oz can be evaluated.