Clean up the tip.json API
Clean up the tip.json API

I've got someone asking to help with building a widget (#21, #41). I
believe this JSON API will enable that.

bountysource/www.gittip.com,studio666/gratipay.com,studio666/gratipay.com,studio666/gratipay.com,MikeFair/www.gittip.com,mccolgst/www.gittip.com,gratipay/gratipay.com,gratipay/gratipay.com,bountysource/www.gittip.com,bountysource/www.gittip.com,eXcomm/gratipay.com,gratipay/gratipay.com,eXcomm/gratipay.com,MikeFair/www.gittip.com,mccolgst/www.gittip.com,studio666/gratipay.com,mccolgst/www.gittip.com,bountysource/www.gittip.com,MikeFair/www.gittip.com,mccolgst/www.gittip.com,eXcomm/gratipay.com,eXcomm/gratipay.com,gratipay/gratipay.com