ENH: Enable conversion of non-Python notebooks to downloadable scripts

[effigies]

This may not be properly guarded; I don't have a lot of Notebooks to test against. Kind of hoping your tests will catch dependency on non-required metadata.

Closes #4.

[coveralls]

Coverage decreased (-0.09%) to 87.5% when pulling c25f317 on effigies:fix/drop_python_file into 3a87e26 on Chilipp:master.

[coveralls]

Coverage decreased (-0.09%) to 87.5% when pulling c25f317 on effigies:fix/drop_python_file into 3a87e26 on Chilipp:master.

[coveralls]

Coverage decreased (-0.09%) to 87.5% when pulling c25f317 on effigies:fix/drop_python_file into 3a87e26 on Chilipp:master.

[coveralls]

Coverage decreased (-0.09%) to 87.5% when pulling c25f317 on effigies:fix/drop_python_file into 3a87e26 on Chilipp:master.

[Chilipp]

Coverage decreased (-0.09%) to 87.5% when pulling c25f317 on effigies:fix/drop_python_file into 3a87e26 on Chilipp:master.

Sorry, I increased the threshold for coverage checks. You can ignore this failure

[Chilipp]

Let me know, when you are done with it and need any review or work from my side. Thank you for the contribution 😃

In any case, I would add a non-Python notebook here and a test for it

[effigies]

This is ready for review. It works for me, and doesn't produce any obvious errors in the test output.

[effigies]

Oh, sorry, just read:

In any case, I would add a non-Python notebook here and a test for it.

Sounds good.

[effigies]

Okay, this is ready for review. Docs build locally, if not very prettily:

[Chilipp]

Awesome! Thanks a lot @effigies for your input! 👍 I added the bash_kernel package to be installed on RTD (otherwise building the docs will fail) and I added some tests for your bash example. When the tests pass, I will merge this PR.