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