Basic and extendable API for patients

A simple API using django-rest-framework to full-fill #3.

# What's changed:
* Add token authentication
* Add a patient serializer
* Add a patient API viewset
* Add URL endpoints `api` and and `api/patients`
* Add search on patients ex: `api/patients?search=Jane`
* Add filter on patients ex: `api/patients?alive=True`
* Some basic documentation in README.md in `api/`
* Some basic tests

# What's next
* Wait on feedback, add more filters, more search parameters?
Unfortunately it doesn't:

> When using boolean fields, you should use the values True and False in the URL query parameters, rather than 0, 1, true or false. (The allowed boolean values are currently hardwired in Django's NullBooleanSelect implementation.)

From the [django-rest-framework docs](http://www.django-rest-framework.org/api-guide/filtering/#searchfilter)