Typing information and opened event

[gmoneh]

This pull request adds two features to the component:

• Typing information for use in typescript environments
• The documentation makes reference to an "opened" event that is fired when the calendar element is opened. However, the component did not actually fire that event ever. So the emit for the event was added in the appropriate place, and now the behavior of the code matches the documentation.

[coveralls]

Coverage remained the same at 100.0% when pulling 2e20dc6d9be6b1a01f08e2727519425d64a65c62 on gmoneh:master into de0fc75fe6f6572eebf47f94da20716ab7690cff on charliekassel:master.