Add support for Streams API commands

[bobby]

It appears that the XGROUP command hasn't yet been added to command reference.

@comnik and I encountered this issue while adding support for Redis Streams to Carmine (cf. taoensso/carmine#208 and taoensso/carmine#210).

[bobby]

Bump, @antirez.

[bobby]

@antirez Should I open a PR to add this? My team needs this semi-urgently in order to use Streams on our current project.

[tirkarthi]

I think he is on vacation redis/redis#5203 and communication will be minimal. Feel free to raise a PR.

Thanks

[bobby]

@tirkarthi observed that XACK is also missing.

[tirkarthi]

Below commands are also missing and thus they are also missing in help @stream. Adding them before release will help since they are used in the redis-cli

• XCLAIM
• XDEL
• XTRIM

Thanks

[bobby]

@tirkarthi @antirez I've added PR #963 to address this issue, but it needs some review.