bugfix: build_data would not have generated the correct file

build_data got refactored at some point without being tested. It would
not generate the correct char_classes.dat file, because it was saying
that reasonable Latin letters had to be lower than 0x20 (it meant
0x200). There are no letters below 0x20.

Despite this bug, char_classes.dat was correct from a previous version.
Manual testing shows that, with the bugfix, it generates the same
char_classes.dat file that is being distributed.
bugfix: args were mixed up in ftfy.fix_file
docstrings, pep8, and pylint fixes