Include season in AMWG plot set 3 titles.
In dirtree_datafiles, short_name and long_name now depend on the root path in a manner which
recognizes that it is a list.
Add options --path2, --filter2 so there can be two paths and two filters, with a clear correspondence.
We may want to deprecate feature where --path can be a list (multiple values), as well as the
--new_filter and --obs_filter options, but I left those in place without comment.
The command-lne form uses the new --path2,--filter2 in the Options class.
I simplified usage and code by dropping --new_filter, a second options argument, and a default
obs path.  It now prints out what files it is writing to.
There is some debugging code in this version because a --seasons option is ignored (by
something in options.py).