Add comparison method to Element class?

[jacobwhall]

I have been writing tests for a panflute filter, and thinking about how to best validate its output. While the "batteries included" functions like convert_text() are helpful for this task, I would like to directly compare elements. I suggest that we add a __eq__() comparison method to the pf.Element class that verifies that they are identical both in type and in terms of their parameters.

For example, comparing two pf.Doc elements would check that both have identical block sequences, metadata, format, and API version.

assert pf.Doc == pf.Doc # succeeds only if all parameters are identical

Thank you for your consideration!

[sergiocorreia]

Just added this method. I also added a test suite, but haven't tested for correctness as much as I would have liked. So if you spot anything off definitely let me know!

[jacobwhall]

Thank you very much!