Add min and max dates to restrict the dates you can select from

It passes all the tests except the coverage which keeps crashing with a Fatal Error on my machine.
Coverage error is: Fatal error: Cannot read property 'length' of undefined. .length isn’t used anywhere so I assume it is just something broken on my machine. (If anyone knows what this is I would be very happy to know).

Add min and max dates to restrict the dates you can select from. Feature requested in: #3.

You do this by adding minDate or maxDate to the options, valid values are '', 'today' which both use moment() or any valid moments date string.