feature request: parameters for reply templates

[Emmanuel Beffara]

Hello,

Unless I missed something, there is essentially no way to control how
`notmuch reply` formats its template message. The standard behaviour is
adequate except for a few details:

- The attribution line uses a default format which is informative but
  overly verbose for my taste. It would be useful to have a setting to
  control it (something like Mutt's `attribution` settings).

- There is no automatic signature.

- Any part not in plain text produces a line “Non-text part: …” or
  “Attachment: …”, which is essentially useless when writing a reply to
  a message.

- The above is particularly annoying when it comes to replying to
  HTML-only messages, because you get no chance to quote the original
  message in your reply.

I use `notmuch reply` with the default format indirectly, because I use
bower an it delegates the task of preparing replies to this command. I
feel it would make sense to define new settings to handle all this, but
maybe there are good reasons not to?

-- 
Emmanuel