Add force_dispatch option to properties
remove old doc about fixed fmt, short explanations of fmt param
doc: Fixed defaultvalue name in docstrings
doc: Clarified button background_color
Merge pull request #2785 from inclement/button_color_doc

doc: Clarified button background_color
Merge pull request #2764 from kivy/doc_fmt

remove old doc about fixed fmt, short explanations of fmt param
doc: colour -> color
doc: colour -> color fixes
Merge pull request #2787 from inclement/color-colour

doc: colour -> color fixes
add python-dev to rpi build instructions, fixes #2740
Merge pull request #2747 from bionoid/force_dispatch

Add force_dispatch option to properties
doc: tweaks to uix/pagelayout.py
doc: fixed formatting in graphics/vertex_instructions.pyx