uix:Popup add `title_color` property to control the color of the
popup title
Document CanvasBase and Canvas.clear.
doc: revisions to input/providers/mactouch.py
doc: revisions to input/providers/mouse.py
doc: revisions to input/providers/mtdev.py
doc: revisions to input/providers/probesysfs.py
doc: revisions to input/providers/tuio.py
Merge pull request #1429 from Ian-Foote/canvas_doc

Document CanvasBase and Canvas.clear
Merge pull request #1428 from kivy/popup_title_color

uix:Popup add `title_color` property to control the color of the title