During development, turns out, that some incompatibility has been
introduced with lxml and html5-parser binary versions on pypy, with
library which is installed on my system. In case, where incompatibility
occurs, there was no error message, no exception thrown, just as a
result of parsing, lame lxml object has been returned, and performing
method like find() on it causes returning None instead of expected
Element object.
Following information about installation of the html5-library[1], I was
forced to change how ebook-converter is installed. Now, we have to build
and compile lxml on the target system, which is forced by introduced
requirements.txt file. Perhaps, I'll reconsider removing html5-parser in
the future.
[1] https://html5-parser.readthedocs.io/en/latest/#unix
Here is the first batch of modules, which are needed for converting
several formats to LRF. Some of the logic has been change, more cleanups
will follow.
