setting course directory

[kcranston]

We would like to be able to put the course directory for an abc-classroom course into version control. This means sharing the same config file, which currently stores the full path to the course directory. Since the path will not be the same on different machine, we would prefer to avoid requiring the full path in the config. We may be able to just assume that the user is always invoking abc scripts from within the course directory, and throw an error if we don't find a config file in the current working directory.

Caveats:

• abc-quickstart runs in the parent directory of the course directory
• When testing with pytest, abc-classroom commands are not invoked from the course directory (but I think the way I implemented the tests and the read / write methods for the config makes this possible)

[kcranston]

If we want to support having the course directory in version control, we should also remove all the parts in the template config.py where we warn people that none of the parents of template_dir, clone_dir, etc should be git repos.

[kcranston]

We should add some notes to the documentation about sharing course repos in version control and the things that can be tricky:

• relative / absolute paths
• nested git repos