py5 events and improved sketch portal

New Features:

• Py5KeyboardEvent and Py5MouseEvent classes
• User-defined event functions such as mouse_moved() and key_pressed() can take an parameter, and an instance of Py5KeyboardEvent and Py5MouseEvent will be passed when it is called
• New py5jupyter library to contain all of py5's Jupyter functionality
• The Sketch Portal is now interactive

Use of py5 + Jupyter without py5jupyter installed is now deprecated. See the blog post for more information about this release.

Bug Fixes:

• #74
• #78
• #81