NOW
* restructure the header system. I guess that onyl gocr.h should be ever called,
 and it would work both for modules and frontends. It is clumsy?
* change the image structure to a tile system. It is faster, but may be harder to
 code.
* there are two functions performing the same thing: charsetatt and charattrinsert: gotta join
  them in charsetatt
* finish charSplitBegin/End
* finish the bw/gray/color conversions
* how to work with text in contextCorrection
* allow imageFilters to be applied in blocks
* finish boxCharSet and other recog.c functions
* finish API design
* see also the TeX documentation for more

FUTURE
* support multiprocessing (not *very* hard, but some care must be taken)
* check the format string in gocr_charAttributeRegister()
* if more than one charRecognizer is used, some AI to see what's the output