convert documentation

[wkeese]

Create reference documentation based on original dojox/calendar doc.

It involves:

• Convert from rst to markdown.
• Update all the examples to use custom elements etc.
• Update CSS class names.
• Update description of events (https://github.com/dojo/docs/blob/master/dojox/calendar.rst#calendar-events) to use dashes. Remove any mention of callbacks.
• etc.

The rst doc is in https://github.com/dojo/docs/blob/master/dojox/calendar.rst, with images in https://github.com/dojo/docs/tree/master/dojox/calendar.