add RedisReadable and RedisWritable

[Uzlopak]

This PR adds RedisReadable and RedisWritable to ioredis

These are convenient classes, which bring Redis Streams to the Node ecosystem.

[Uzlopak]

I refactored some code of mine, and have to write some unit tests in your format.

To Be done:

• [ ] write unit tests
• [ ] check if maxlen is correctly refactored
• [ ] check if it can be instantiated correctly (is the export in index.ts is enough?)
• [ ] write documentation
• [ ] add objectMode
• [ ] add consumergroup
• [ ] add blocking