Use Beautiful Soup 4

Closes https://github.com/openelections/core/issues/111
Load 2008 Maryland Special Election

Modify datasource and add loader for 2008 special election for the
4th Congressional district.

Addresses https://github.com/openelections/core/issues/107
Finish loading 2008 special election results

Add office, district and reporting level to the raw result.  I forgot to add these in my initial pass.

Fix the determination of the ``Result.write_in`` field so it can handle ``RawResult.write_in`` fields set to ``None``

Add validation for 2008 special election results.

Closes https://github.com/openelections/core/issues/107