#36: I've decided to rewrite tests from robot framework to pytest.
Added dependency to new version of pyDHTMLParser, because of bug in old.

Bug was found during new testing (#36).
#36: Added integration test of aleph.getListOfBases().
#36: Added unittests of aleph; variables, exceptions and DocumentID.
Some of PEP8 aplied.
#36: Added integration tests of all lowlevel API.
#36: Added unittest of tryConvertToInt().
#36: Fixed bugs in docstrings found during unittests.
#36: Added tests of aleph.getISBNsXML() and aleph.getAuthorsBooksXML().
#36: Added tests of all XML getters in aleph.py.
#36: Added tests of the counters. aleph.py is now tested with pytest.
Fixed bug in convertor.py.