Please refer to main plugin script and consider the following notes:

TESTS:
======
- Login
- Enter URL http://<path to roundcube>/?_task=dummy&_action=plugin.calendar_tests

TODOS:
======

- Thunderbird sync (tbclient.php)

  A basic sync client is implemented. It does not fully support recurring events.
  Only daily, workdaily, weekly, bi-/three-/four-weekly, monthy and yearly is
  supported yet. F.e. recur weekly on MO,TU,WE is not recognized and will be
  overwritten in TB by a simple weekly recurrence on sync.
  
LATER
=====
- Re-implement CalDAV (M. Duelli)
- Implement Google API backend