Allows you to use CAS server as a means of authentication to your SchoolTool
application.

Deployment
----------

Here is what it takes to get CAS deployed:

1) schooltool.cas needs to be in the path (whether as an egg or as
   part of a sandbox)
2) a slug called schooltool.cas-configure.zcml needs to go in the
   instance/plugins directory with contents::

    <include package="schooltool.cas" />

3) the following needs to be added to schooltool.conf (substitute your
   own server for the sla example)::

    %import schooltool.cas
    <cas_authority>
      server https://sla.mics.me/
    </cas_authority>
