Document ad-hoc API for election description classes

Addresses https://github.com/openelections/core/issues/36
us.md.validate as package

I want to load expected candidate counts from a CSV fixture and
want to package it in the validate directory.

Addresses https://github.com/openelections/core/issues/36
Add validation for 2002 Maryland primary

This required a lot of changes.

First, because there were State Senate and House of Delegates
contests, there were a ton of candidates.  I set up a mechanism to
load the candidate counts from a fixture.

I also added lists and mappings for the State Senate and House of
Delegates to ``us.md.jurisdictions``.

The mappings from Congressional District to county changed from
2000 to 2002, so I had to define these differently in
``us.md.jurisdictions``.

Finally, I changed the keys in district mappings from integers to
strings.

Addresses https://github.com/openelections/core/issues/36