Guizero

- Various bug fixes
- wrapping multiline `TextBox` data
- `ButtonGroup`, `ComboBox` now allow 0 options at init
- Minimum pillow version is now 4.3.0
- `update` method added to `Add` and `Window`

https://lawsie.github.io/guizero/changelog/#053-2018-07-18

ListBox, cascading properties and a few bits and bobs

https://lawsie.github.io/guizero/changelog/#050-2018-04-10

- Fixes bugs in TextBox and PushButton to do with failed imports from tkinter
- Fixes a bug in Text where there were still references to string_var which didn't exist

- Add Waffle class
- Update all docs to new import style
- Add check for Python 3 in setup.py
- Fixes broken add_option in Combo

- Add enable/disable/toggle for PushButton - thanks jezdean
- Add App on_close() method and document destroy method from tkinter - thanks jezdean
- Change orient parameter in Slider/ButtonGroup to horizontal (boolean) - thanks bennuttall
- Add documentation .md files in docs-src/docs for contributors
- Add background colour and bgcolor() method to App
- Add installation instructions for Mac to docs
- Fixed a bug with error formatting in Picture