Exporter changes, use dictionary comprehension

The format for creating the properties dictionaries in the _crawl_fig and _crawl_ax functions in the exporter module now use dictionary comprehensions along with the getp function from matplotlib.

No problem if you don't want to pull this one in, but I thought it might be a concise way to do the same thing. 

Also, I don't think that there should be any compatibility issues from this since previously undocumented keywords are added back to the properties dictionaries.