Adds 2018v3.0

This allows processing of files in schema v 2018v3.0. (0.2.4 allowed version 2018v3.1, but apparently 3.0 is also in circulation).

Start of 2018

This release updates irsx to allow "dumb" processing of 2018v.3.1; they will be processed according to pre-2018 rules. Any unknown xpaths are logged to the keyerrors list, which is visible from the command line with the --verbose switch. Another update, expected within the month, should update the metadata to use the new 2018 TY schemas, once they are processed.

v0.2.1_update_2017

This update should support tax year 2017 schemas 2.0, 2.1, 2.2, 2.3. At present settings.py includes a listing of each legal version, but we're likely to switch to a listing of legal years.
see more about the metadata changes here jsfenfen/990-xml-metadata@20255e4
and here jsfenfen/990-xml-metadata@d2f58d6