Feature/arm models

#### Summary:
Fixes issue #707. I also added a note on the wiki page for the ARM models stating that there is some missing/different data so some of the models are slightly different. 

#### Intended Effect:
Implement models from ARM in Stan.

#### How to Verify:
See src/models/ARM/

#### Side Effects:
None since code does not touch any other parts of Stan.

#### Documentation:
Wiki page