added create util for rental agreements endpoint
Merge pull request #38 from BookingSync/create_a_new_rental_agreement

added create util for rental agreements endpoint
Add support for fetching associations
Get rid of json extension in vcr cassettes
Add rates support
Fix specs/docs, sawyer has been removed
wip - green specs
wip
wip - doc
wip
wip - response docs
wip
wip - fixed specs, delete fix
wip - docs improvements