Add keyword inputs

[8bitsam]

Closes #66, #68 (did a quick fix for this) The cookiecutter now prompts the user with three keyword questions, which default to blank. The following is the git diff of pyproject.toml with the diffpy.utils description. The only notable difference is single quotes vs double quotes, which is just an artifact of the cookiecutter input and probably can't be easily changed. It shouldn't matter though.

Also, a result of this is that test_utils.py had to be updated, so if this is merged everyone should definitely sync right away.

[Sparks29032]

Can the user provide keywords in a comma-separated list?

Then we can directly put this into the keywords list.

[sbillinge]

We def didn't want 3 new questions

[sbillinge]

nice work!