align error/help message wording with manual pages
config: auto-detect $TORK_CONFIGS values only once
faster globs on slow FS via Dir.glob() block-form
add `list_failed_test_files` command, bound to `l`

https://github.com/sunaku/tork/pull/60
engine: emit test file counts in :idle event data
engine: emit actual test files in :idle event data
engine: only list most recent test files in :idle
tork: emit "tork:" prefix on messages sent to user
tork-runner: percentage lied; print counts instead

The percentage of completion is not accurate because it only measures
how many tests that have started running _so far_ have been completed.
This makes the percentage jump from 100% to lesser values as tests run.

Also drop the `tork-runner:` prefix from progress messages and replace
VT100 escape codes for reprinting in-place with a \r (carriage return).
shorten all status message tokens to ~4 characters

* In tork-driver(1):
  * `reabsorb` is now `over`

* In tork-engine(1):
  * `idle` is now `done`
  * `pass_now_fail` is now `fail!`
  * `fail_now_pass` is now `pass!`

* In tork-master(1):
  * `absorb` is now `boot`
shorten all commands names down to ~4 characters

* In tork-driver(1):
  * the `run_all_test_files` command is now named `test!`
  * the `over` message is now named `boot!`

* In tork-engine(1):
  * the `reabsorb_overhead` command is now named `boot!`
  * the `run_test_file` command is now named `test`
  * the `run_test_files` command is now named `test`
  * the `stop_running_test_files` command is now named `stop`
  * the `rerun_passed_test_files` command is now named `pass!`
  * the `rerun_failed_test_files` command is now named `fail!`
  * the `list_failed_test_files` command is now named `fail?`
  * the `over` message is now named `boot!`
engine: add `test?` and `pass?` listing commands