Refactor Kitura-redis and document all of the current APIs

[shmuelk]

Refactor the Kitura-redis code base to have smaller and more manageable files and complete the API documentation of the existing Kitura-redis API set.

Description

The Kitura-redis Redis.swift and RedisMulti.swift files have been brokn up in a main file and set of extensions.

Motivation and Context

Make it easier to maintain Kitura-redis and add API documentation to make it more consumable.

How Has This Been Tested?

Ran the Kitura-redis unit tests.

Checklist:

• [ ] I have submitted a CLA form
• [ ] If applicable, I have updated the documentation accordingly.
• [ ] If applicable, I have added tests to cover my changes.