This makes skipping/unskipping tests easier, and improves readability
a bit.
Note it's also possible to just write the test name with no preceding
function, when the type is constrained (see Journal.hs).
Limiting to just the file(s) you're interested can make doctest start
much quicker. With a big caveat: you can limit the starting files,
but it will also test all other local files those import.
--slow turns off doctest's --fast flag, which skips reloading between
tests.
--verbose shows progress output as tests are run, if doctest 0.16.0+
is installed (and I believe will be harmless otherwise)
