Write feature detector to determine angle of base line of text on a shred.

[dchaplinsky]

In addition to line detection we would like to determine angle of text baseline on shreds.
This can be a valuable feature on it's own, because angle of a baseline is constant across the page and it might differ from 0 degrees because document was printed/shredded under slight angle.
It also can determine position of each line on a shred (so we can use this to match it to another shred), number of lines, presence of text, etc.

Thanks to @fednep we have a solution that should be polished a little bit.
Areas of improvement are:

• Adaptive binarisation similar to one that @xa4a ported in terms of Write a feature detector to find fragments of lines on shreds. #10
• Better accuracy
• Heuristics to suggest tags like has text, etc
• It should also return positions of text lines in relation to shred side
• Ideally: some way to evaluate algo using ground truth dataset.

[dchaplinsky]

Is under development in #5