fixup! OCR: Support tesseract writing to files with any extension
fixup! OCR: Add ability to pass configuration to tesseract
fixup! OCR: Add ability to pass user_patterns and user_words to tesseract
fixup! documentation: Add OCR tips

This way the code snippets in the document can be tested with:

    nosetests --with-doctest --doctest-extension=.md ocr.md

TODO: Test this from `make check`? But we'll need to find a way to
disable the doctest based on tesseract version because on my system
the above command raises this:

    RuntimeError: tesseract version >=3.03 is required for
    user_patterns. version 3.02.02 is currently installed
fixup! documentation: Add OCR tips

(Table is easier to read in markdown format. This format is supported
by github flavored markdown, and by kramdown in case we want to publish
this article on stb-tester.com.)
fixup! documentation: Add OCR tips

(Fix markdown syntax for images.)
fixup! documentation: Add OCR tips

(General editing of the prose.)