Fix make sphinx-texinfo warnings:
WARNING: undefined label: notmuch-jump (if the link has no caption the
label must precede a section header)
WARNING: undefined label: notmuch-saved-searches (if the link has no
caption the label must precede a section header)
While adding that fixed (also other) typos noticed by aspell(1) run,
and capitalized Emacs and (most) Notmuch terms to match how emacs
Info documentation seems to look in general.
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.
