Now that it's easy to add argument specific modifiers in opt
descriptions, add a new .allow_empty field to allow empty strings for
individual string arguments while retaining strict checks
elsewhere. Use this for notmuch insert --folder, where the empty
string means top level folder.
Enable override of the index.try_decrypt setting on a per-message
basis when invoking "notmuch insert".
We also update the documentation and tab completion, and add more tests.
The post-new hook might no longer be needed or run very often if
notmuch insert is being used. Therefore a post-insert hook is needed
(arguably pre-insert not so much, so don't add one). Also add the
--no-hooks option to skip hooks.
Add --keep option to keep any remaining stuff in index or file. We
could distinguish between failures to index and failures to apply tags
or maildir sync, but for simplicity just have one.
This is the output from sphinx-quickstart, massaged a bit, along with
our existing man pages converted to rst.
A skeleton notmuch-emacs manual is also included. It is not suitable
for end user use yet.
