Widgetastic.patternfly

First 'official' release, significant number of widgets and tests have been authored, and the library has been under consistent use for some time now.

This release does not support py2.7, as previous releases did.

Support for py3.5, 3.6, and 3.7 is included in CI matrix.

Tagged to test travis -> pypi deployment

New methods:

`BootstrapNav.all_options`, returning a list of strings

`Button.text` and `Button.read()`, returning text content of Button element.

PF Modal definition

Add hover property for Dropdown