Added new query: DocumentQuery.

Bump #24.
Added settings.DEFAULT_LIBRARY.

Bump #24.
DocumentQuery added to uml.

Bump #24.
Changed documentation namespace. Documentation extended and cleaned.

I've tried to add documentation for DocumentQuery, but it broken down, so
I had to clean it.

Bump #24.
Fixed test subsystem.
Export test commented out.
Added documentation for aleph/convertor.py
New version - 1.5.1.

Fixed #24.