Fixed example code for populating a tree view, replacing it with code for a minimal working example.
Changed the example app to fit preferred approach in new programming guides.
Removed inmports and main view bits, to reduce to minimum example.
Merge pull request #963 from geojeff/treeview_docs

Fixed example code for populating a tree view, replacing it with code fo...
textinput: ensure others dependent values from self._lines are updated before assigning a new self._lines. Otherwise, the text property is triggered, and bad magic will happen. closes #950
Merge branch 'master' of ssh://github.com/kivy/kivy
doc: extend size/pos_hint explanation in widget.rst in guide2