Extensions to shellwhat testing.

In the course's requirements.sh, add

# replace 0.0.1 with the appropriate release version
pip3 install --no-deps shellwhat-ext==0.0.1

To use the extensions in an exercise's SCT, import the function you want into the SCT block of the exercise:

from shellwhat_ext import test_cmdline
Ex() >> test_cmdline([['wc',   'l', '+']])

Follow these steps

1. Open a PR, merge into master when appropriate.
2. Once merged, increment __version__ = 0.0.1 to reflect changes (see semver for guidance).
3. Create a github release labeled vVERSION. E.g. v0.0.1. (see here).

make install
make test