Reminders

Added the ability to set reminders for events. You can either use the regular event initializer

    @event = Event.new :start_time => "2012-03-31", :end_time => "2012-04-03", :reminders => [minutes: 6, method: "sms"]

or add it as part of a block

    event = cal.create_event do |e|
      e.title = 'Some Event'
      e.start_time = Time.now + (60 * 10)
      e.end_time = Time.now + (60 * 60) # seconds * min
      e.reminders << {method: 'email', minutes: 4}
      e.reminders << {method: 'alert', hours: 8}
    end

It'd be nice to pack this into a reminder class and make things a little more idiomatic, so you could say
    
    e.reminder do
      r.method = "email"
      r.minutes = 10
    end

But it works well enough as is. I added a few tests for reminders too.