Clarify purpose of BaseLoader in docstring
Clarify purpose of BaseLoader in docstring

Add notes to BaseLoader docstring that clarifies that it should:

* Create RawResults
* Only do minimal data cleaning/transforming such as striping
  whitepspace and converting vote counts to ints.

Also remove unused imports.

Addresses #49

openelections/openelections-core,cathydeng/openelections-core,cathydeng/openelections-core,openelections/openelections-core,datamade/openelections-core,datamade/openelections-core