removed leftover cruft
some more old leftovers removed
Merge remote-tracking branch 'upstream/master'
rename references to plain "SDL" to "SDL1_2"
switch SDL input handling over to FFI (still SDL1.2)
SDL 2.0 support

this is a straight-forward migration from the SDL 1.2 code we had
before.
add a simple switcher for SDL 2.0 / SDL 1.2

if present, we prefer SDL 2.0 over SDL 1.2
Merge remote-tracking branch 'upstream/master' into SDL2

Conflicts:
	koreader-base
fix concatenate 'int64_t' and 'string' in dbg.lua
Merge pull request #111 from hwhw/SDL2

SDL2 support