Merge pull request #264 from koreader/chrox-master

fix missing default waveform mode
convert pic_jpeg interface to pure Lua/FFI solution

pic_jpeg had a wrapper lib before that was needed because of the
libjpeg API which uses setjmp/longjmp error handling.
By using the TurboJPEG API that comes with libjpeg-turbo, we can
use a pure Lua/FFI based approach.