async & sync support

[0x8f701]

it'll be good to support both async and sync, although this crate's name is async hhh, but sync can enable more complex application logic and trees etc

[0x8f701]

I made a sync version in my fork: https://github.com/GopherJ/rsmq-sync but eventually need to find a way to switch between async & sync.

[0x8f701]

https://github.com/fMeow/maybe-async-rs is an option but redis's interface isn't very format. it has invoke_async and query_async

[DavidBM]

Added a new sync facade. Let me know if tha works