Simplify convictions_data/statute.py

[ghing]

This is related to sc3/cook-convictions#35. Now that sc3/python-iucr#3 is implemented, allowing lookup of ILCS references that include subsection bits, see if we can simplify/clean up the code in convictions_data/statute.py and code more of the statutes in our dataset.

Ulitmately, if the parsing code seems simple enough or it's easy to abstract it to different ILCS formats, we could move this to the iucr package to close sc3/python-iucr#8, though that still seems like a low priority to me.

[bepetersn]

Some of the functionality currently in statute.py should be pushed into the ilcs package. See the issue from that repo: sc3/python-ilcs#2

[bepetersn]

Also related to this, iterate over the ILCS and ILRS codes we currently aren't matching to try to improve our regexes / parsing: #7.