Adding the Reply-To header, and having a ponder.
Moving the headers into their own module.

--HG--
rename : gs/group/list/sender/replytoheader.py => gs/group/list/sender/headers/replyto.py
rename : gs/group/list/sender/simpleadd.py => gs/group/list/sender/headers/simpleadd.py
rename : gs/group/list/sender/subjectheader.py => gs/group/list/sender/headers/subject.py
Passing the full email to the modify_header method of the Header classes.
Adding a docstring
Ooops, updating the configure.zcml
Adding the From header (which parses, at least)
Modules cannot be called from.
Starting the unit tests for the From header
Working through the tests.