Added a batch processing example

[mtb-za]

A basic implementation of batch processing of fold data. This script accepts a list of datafiles and will plot the poles, then calculate and plot the fold axis and the axial plane of the fold.

[joferkington]

Sorry for my delay in replying to this! Thanks a ton for submitting the example!

There's one caveat -- I use the examples as integration tests. The test suite generates an image for each example and compares it to a saved image.

As it stands, this example won't play well with the test suite (mostly because it generates output files). I can definitely change things to make it work, but there's more than one way to handle it. I've been putting off merging this until I have time to think through it. (For example, it would be easy to just not have it generate output images, but that would make it a less useful example.)

Regardless, it's a great example, and I'm definitely going to merge the pull request, I just need to think through the best way to integrate it into the test suite.

Thanks again for submitting it!