sdl2: start to write a new window provider based on sdl2. sdl2.pxi has been created from the ignifuga game engine, but maybe functions and definitions are missing. Need to create a generator out of it. At some points, window_sdl (used currently only on iOS) should be removed.)
sdl2: add missing window_sdl2 files, and correctly implement 'auto' fullscreen. read all the missing window event too.
sdl2: add sdl2 image core provider (not complete, need more conversion format, and save support)
sdl2: support for text rendering
sdl2: ignore generated .c
sdl2: fix ignore
sdl2/text: fix color bgra -> rgba
core:sdl2 clipboard provider
Merge branch 'master' of https://github.com/kivy/kivy
Merge remote-tracking branch 'upstream/master'
- convert data to a bytearray to more consistently get color info accross
  python versions
add debug method for recursive updates
fix nested scrollviews and add passoff functionality
Add SmoothLine reload_observer. Fixes #2377.
switch to dispatch_generic and fix scroll cancel
make textinput play nice in scatter and scrollview
Bring sdl2 in line with current master and other fixes to make things usable. Sponsored by ScramSoft.
remove unused __init__ from checkbox
doc: added warning tag for better formattimg

Including the experimental code warning in the verison role makes the
HTML really ugly. Moved to a dedicated warning role.
doc: revisions to adapters/adapter.py

Added links to properties