Don't call notmuch after every mail sync

It's a bit slow, and I rarely perform searches with notmuch
anyway. It's not worth doing it every time.
emacs: don't open scratch in markdown-mode
mutt: open plain text attachments in emacs
Add a utility to generate simple line graphs

plot takes two whitespace-separated columns, charts them with gnuplot,
and dumps the result into "output.png". Convenient!