MAINTAINERS: Add additional checking to check-MAINTAINERS.py

In order to maintain the new sorting, add a number of additional checks
to check-MAINTAINERS.py.  In summary, these are:
- arrange to sort names by surname and then forname(s).
- rework the code to use regex matches for the fields to accommodate
some fields that spill over into the next column.
- arrange to sort by more than one field.

contrib/ChangeLog:

	* check-MAINTAINERS.py (get_surname): Rename to ...
	(get_name_for_sort): ... this.  Add the forenames after the
	surname.
	(check_group): match against regexs and support additional
	fields for secondary sorting.
	(sections): Rework to use regexs, add rules for the other
	sections in the MAINTAINERS file.