Move release note preparation into a callable Rake task
Move release note preparation into a callable Rake task

There is a regression here, and there has been for a couple of releases,
so to make it easier to debug, let's make the note preparation callable
with `rake notes`.

mtimkovich/command-t,wincent/command-t,wincent/command-t,mtimkovich/command-t,wincent/command-t,yrro/command-t,yrro/command-t