Implement a test runner for lfetool

[oubiwann]

This will essentially be a formatter + a function to run the tests with the provided formatter.

This should be made flexible so that users can provide their own formatters and use them easily with the test runner.

This comes as a result of the investigation done in issue #85 in support of issue #61 and issue #83.

From a comment in issue #83, inspiration may be found here:

• http://stackoverflow.com/a/11031019
• https://github.com/seancribbs/eunit_formatters/blob/master/src/eunit_progress.erl#L5

[oubiwann]

Got a start on this with the latest commit in 2660001 and the preceding 8 commits.