Python importer

[cboulay]

No guarantees this works. The API may change. But please test!

[cbrnr]

Very nice to see some Python code here! I've ran the code through some quick test files. For a first version I think this works very well.

A few things could be changed though. For example, I suggest to use the logging module to do all the logging stuff which is now done with the print function. In addition, verbose should really be False by default as described in the docstring.

Furthermore, I don't know if the use of defaultdict is really necessary. Printing defaultdicts is not really nice because the output includes a lot of boilerplate strings. I haven't looked at the code closely enough, but maybe it is possible to use normal dicts instead of defaultdicts. Furthermore, many entries are one-element lists, which makes accessing these elements rather difficult. We should check if lists are really necessary for all fields or if there are fields that can only have one entry - in that case, we could get rid of these one-element lists.

I'd prefer the docstrings to adhere to the numpydoc format.

I'd be happy to contribute if you want. I suggest to merge this PR into master if there are no serious bugs (and so far I don't see any) so that we can deal with changes in separate PRs.