Document configuration items in manpage

This adds current items to the "CONFIGURATION" section in r2e.1, manually
extracted from rss2email/config.py.

Signed-off-by: Etienne Millon <me@emillon.org>
CHANGELOG: Document this branch

Signed-off-by: W. Trevor King <wking@tremily.us>
r2e.1: Fix 'massage' -> 'message' typo

Port 74ea4b7 (config: Fix 'massage' -> 'message' typo, 2013-09-29)
into this branch.

Signed-off-by: W. Trevor King <wking@tremily.us>
Merge branch 'config-manpage'

This is not very DRY, but it gets the job done for now.  If it turns
out to be a pain to maintain, I may try to automate the extraction
later.

* config-manpage:
  r2e.1: Fix 'massage' -> 'message' typo
  CHANGELOG: Document this branch
  Document configuration items in manpage

Signed-off-by: W. Trevor King <wking@tremily.us>