clean import, reduce log and better progress bar.
add tests file ex.py and test.py...
add 'mutation apply UID'.
do not show mutation during test, but during replay.
v0.3.1 with python 3.7

- Check the database exist.

- play_test_tests: pass extra argument `command` for replay...

- Specify numprocesses only when max workers > 1.

- During `play` store command for re-use in `replay`.

- Count mutation failures.

- replay: re-use command.
mutation: ignore files without coverage.
alpha is the time taken to run the tests
sort files by size before computing mutations...

... it is better, because big files will take a lot of time to
complete, whereas small file will do fast, that way we can maximaze
the time where the pool is busy.

- duplicate source command before using it, to avoid accumulating

- Improve wording.

- Less TODO.

- Less or no need for benchmarks.

- repository is a git repository not the index.
small refactor.

- add missing replay command in docopt.

- fix sampling return values.

- allow float as sampling.

- display success message only in case of success.

- replay: fix max_workers=1 until further notice.

- replay: show mutation once.

- replay: uid is useless.

- replay: lookup the good subspace for failed mutations

- cli: it is possible to pass pytest argument file-or-directory
  without going throught the ceremony of copy pasting the whole

- add tqdm to show progress.

- bump v0.2.9.

- print output to stdout.

- only give a summary of ignored mutations.

- not interesting != interesting.

- drop the delta.isspace() it never happens.

- rename mutation_tess to mutation_pass, reverse again the logic to
  return False when mutation fails.

- PYTEST: no tb, with summary.

- database_open accept a string or Path.

- run returns an integer.

- add replay command to help with debugging.
refactor + black + isort.
replay mockup
store mutation failures.