fix blitbuffer rotation

blitbuffer rotation was broken in two places:
- actual coordinate translation
- blitFromRotate function
add framebuffer module using FFI for SDL/Emu mode

it seems to work fine even though the input part is still handled
in a classic Lua/C API module
Merge pull request #89 from hwhw/fix-blitbuffer

fix blitbuffer rotation
fix fail on init of tesseract
Merge pull request #90 from hwhw/framebuffer-sdl

FFI module for SDL framebuffer
Merge pull request #91 from houqp/houqp-master

half done ffi pic module
Merge pull request #92 from chrox/master

fix fail on init of tesseract
use more precise RGB to gray conversion

we use this:
gray8 = rshift(4897*red + 9617*green + 1868*blue, 14)
Merge pull request #93 from hwhw/blitbuffer-conversion

use more precise RGB to gray conversion
add back missed sample jpg file for unit test
fix: convert emulator dimension from string to number

* also add comment in blitbuffer module