Many of the external links found in the notmuch source can be resolved
using https instead of http. This changeset addresses as many as i
could find, without touching the e-mail corpus or expected outputs
found in tests.
Currently, http://packages.python.org/notmuch/ goes through a series
of redirections and ends up pointing to readthedocs. Since we're
using readthedocs directly anyway, just point to it directly.
readthedocs are also now sensibly using a separate domain
(readthedocs.io) for their hosted documentation as distinct from their
own domain (readthedocs.org), so use the correct tld.
The old instructions were telling users to do "easy_install cnotmuch"
which installed some old, stale bindings. The new instructions should
be much more effective.
