Handle Kobo backlight via FFI instead of Lua/C API
Merge pull request #101 from hwhw/kobolight-ffi

Handle Kobo backlight via FFI instead of Lua/C API
adaption of Lua/C-API for ffi KOPTContext
add ffi KOPTContext module
install tesseract data in travis
fix type of ocr_type variable in libk2pdfopt
add missing test PDF file
install tessdata into right place
Update .travis.yml
export TESSDATA_PREFIX env in travis
get rid of getPhysicalRect in lightenRect
since coordinate of each pixel is already transformed in setPixel
add rotation tests in blitbuffer spec