Write Swagger documentation for API

[AlexSuth]

This issue creates the Swagger API documentation for our Users/Tasks application.

The easiest to test the code is to plug the code into the Online Swagger Editor, which will create a graphic representation of the API and will spot any errors.

To Test:

1. Copy the code from /docs/swagger.yaml
2. Paste the code into the online Swagger Editor
3. The right hand side of the screen will populate with details from my provided code.

Activity	Time Spent
Swagger research	1.5 hr
Testing endpoints and noting responses	1 hr
First draft	2.5 hr
Revisions	2 hr
Documentation	.5 hr