Added script to extract all genes from a given LOVD URL.
Updated out of date documentation.
Changed if results is not None to more compact if results when checking regex search results.
Changed general exceptions to NotImplementedError in abstract LeidenDatabase methods.
Refactored error handling during data extraction and saving. Removed unused variables leftover from previous implementation.
Replaced use of namedtuple with tuple to match common practice.
Merge pull request #3 from andrewhill157/extract_data

Added script that extracts all data tables from specified database.