Update URLs to https://, for the API itself and its documentation

This updates URLs for the API docs to use `https://` (which they redirect to anyway), and to the API itself, which [strongly encourages the use of HTTPS](http://sunlightfoundation.com/blog/2014/01/28/encrypting-our-congress-api-and-protecting-your-location/).

I haven't tested these changes out, I've just done some find/replace. I filed a similar pull request over at https://github.com/lobostome/FurryBear/pull/2, and the maintainer needed to pull in a certificate bundle to make it work. I'm not sure if that's necessary here, but it's true that I'm not very familiar with PHP practices today.