Add --min-duration-to-report option

[brandonchinn178]

Fixes #341

Not sure how to write a test for this, but the following manual tests work:

# shows some tests with (1.21s or 0.02s duration)
(cd core-tests && stack run -- tasty-core-tests)

# shows all test durations
(cd core-tests && stack run -- tasty-core-tests --min-duration-to-report 0)

# shows no test durations
(cd core-tests && stack run -- tasty-core-tests --min-duration-to-report 1m)

[Bodigrim]

Wrt tests, I imagine one can add a test suite and a shell script, which runs tests and compares stdout against a golden file.

[VictorCMiraldo]

Thanks for adding the issue number to the changelog :)

[Bodigrim]

Thanks @brandonchinn178!