Maxime Pineau

Adding `zunionstore()` and `zcount()` methods. `predis` documentation states that `zcount` returns a string, but that's not the case

This pr adds `watch()` and `unwatch()` support. The methods don't do anything, like `eval()` and `quit()`.

This pr tries to stick with the redis documentation, which states that most of the `xxxget()` methods should return string values - `get()` - `hget()` - `hmget()` - `hgetall()` -...

The `scan()` method does not work when a slash character `/` is used in a key or in the match pattern. The reason behind this is because the character `/`...