Added location search to api

I was recently trying to use your api and was frustrated by the lack of capability to search by location, so I've now added that capability. It returns the nearest bathrooms ordered by distance from the given location in the same way that your client-side page does.
![screen shot 2014-06-24 at 4 55 03 pm](https://cloud.githubusercontent.com/assets/5298929/3377685/f82669dc-fbe1-11e3-93c4-e458bc7bc2e6.png)

also, in the general api call, the parameter was unirsex rather than unisex, so I changed that, but I realize that may mess up anyone already interacting with the api, so I can change that back if you'd prefer.

I also noticed that code coverage is important to you, so I added the gem simplecov which attaches to rspec and tells you which lines of code are tested and which aren't, what your overall coverage is and what your coverage is per file.

Prefer single-quoted strings when you don't need string interpolation or special symbols.