Harvest data from CONTRIBUTORS.rst files

[ageorgou]

Some projects use files named CONTRIBUTORS.rst or AUTHORS.rst to record contributors. These are not fully standardised, but contain information that could be used to populate the metadata output.

Since the name is not always constant, perhaps haggis harvest could accept another option pointing to the file.

[sdruskat]

This sounds like a good idea. We may not come to this during the first iteration of the research project, but mining files like this is definitely something we plan to look into.