Crude support for BITFIELD/BITFIELD_RO

[CharlesRaymond1]

There's no current way to support the use case where we want to have support for -ASK or -MOVED with the BITFIELD command. The sole option is to send the BITFIELD command to a single node having the knowledge where this specific key resides (as explained in #50 ). This forces the client to have a sub-optimal flow when using the command.

As the BITFIELD command will always apply to a single key (single slot), there is also no need to parse the sub-commands. Also, redis executes all bitfield sub-commands in the same execution (see https://github.com/redis/redis/blob/unstable/src/bitops.c#L1136)

Optionally, we can support the BITFIELD_RO as a bonus because the only difference is that it supports the GET command.

[CharlesRaymond1]

Created draft PR: #96

[bjosv]

Closed by #96
Thanks!