Fix hocr-combine, hocr-eval, hocr-lines and add more tests

• Fix hocr-combine: Delete the function call to importNode which does not exists in etree and seems not necessary anymore.
• Fix hocr-eval: The function get_text of this file failed in Python 3 and we use now the same code of this function as in the other tools.
• Fix hocr-lines: It was outputting byte strings in Python 3.
• Add tests for hocr-combine, hocr-eval, hocr-eval-geom, hocr-lines

See details: v1.1.0...v1.1.1