Fixed some old code, small improvements.
aleph.py: Added new function download_records().
Added four new functions. Refactored few unnecessarily long variables.

 - getISBNsXML()
 - getAuthorsBooksXML()
 - getPublishersBooksXML()
 - getBooksTitleIDs()
Fixed bugs in aleph.py.
convertor.py: Added new function getDocNumber().
__init__.py switched to use aleph.downloadRecord().
Fixed #27 - parsing of internal url field.
convertor.py refactored slightly, fixed few little bugs.
Changelog updated to version 1.6.0.