release 1.0.0

This is the first Python 3.7+ release which is also compatible with the
latest IPython version.

Merge pull request #76 from gnestor/event-handlers

Move event handlers out of attributes

include button, label, and style components

allow VDOMNodes to be null

Merge pull request #6 from nteract/improve-api

make naming conventions match that of other libs

clean up readme and initial samples

outline how to make a release