make membership role configurable
Add a slot for legislator role
Switch to getattr
Only remove the role attribute if the object has it
Set default role more sanely
Allow setting Legislator#role in initializer
Underscore _role, since it gets deleted
Add links to Membership model
Merge pull request #54 from jpmckinney/links

Add links to Membership model
Merge pull request #46 from jpmckinney/role

Make membership role configurable