Add hashmap to redis args

[gibranamparan]

This is adding the std::collections::HashMap as a ToRedisArgs so that now would be possible to run HSET commands using a simple HashMap (as it already supports for BTreeMap)

Fixes #444.

[shachlanAmazon]

Can we allocate capacity ahead of time? in large maps this might have significant perf cost.

https://morestina.net/blog/1843/the-stable-hashmap-trap

[djc]

Seems reasonable. @jaymell any thoughts?

[djc]

Can we allocate capacity ahead of time? in large maps this might have significant perf cost.

https://morestina.net/blog/1843/the-stable-hashmap-trap

This is only a ToRedisArgs impl, writing out the HashMaps items into Redis args. Seems to me that the capacity issue you're referring to would only be relevant for a FromRedisValue impl.

[shachlanAmazon]

Can we allocate capacity ahead of time? in large maps this might have significant perf cost.
https://morestina.net/blog/1843/the-stable-hashmap-trap

This is only a ToRedisArgs impl, writing out the HashMaps items into Redis args. Seems to me that the capacity issue you're referring to would only be relevant for a FromRedisValue impl.

Oy, you're right 😵‍💫

[jaymell]

The PR does not compile....

[gibranamparan]

The PR does not compile....

This should compile now.

[jaymell]

Thanks!