Scraper documentation and refactor
Scraper documentation and refactor

- Simplification of get_proposals_since using generators

cityofsomerville/citydash,cityofsomerville/cornerwise,cityofsomerville/citydash,codeforboston/cornerwise,cityofsomerville/cornerwise,cityofsomerville/cornerwise,codeforboston/cornerwise,cityofsomerville/citydash,cityofsomerville/citydash,codeforboston/cornerwise,cityofsomerville/cornerwise,codeforboston/cornerwise