Todo is now Reminder

The former was used by the calendar app, when reminders lived there.
Update alarm fields
Merge driver and session
Refactor

I'm trying to make the low-level Session methods more closely resemble
the remote API.
Move low-level stuff into Records module
Refactor again
Move test dependencies to Gemfile
Add script/test runner
Recommend --path=vendor and --binstubs
Apply changesets as they are received

The server can send back changesets at any time, so we must check for
them every request. This actually simplifies adding and updating
reminders, since we receive a new copy of them straight away, and don't
have to update the pool ourselves.
Ignore /vendor and /bin

I keep my scripts in ./scripts, and leave ./bin for bundler binstubs.
Add update tests