Add the ability to use bash variables when setting keys

[fattredd]

Now we can run

$ test="a b c"
$ kvset key 1 2 3 4 $test
$ kvget key
> 1 2 3 4 a b c

This is very helpful when using kv-bash for storing arrays.

[damphat]

Good idea Jack!

Although your idea is good, but it does change the API signature.

Let me think more about it before merging because it might effect someone else who used the API.

[fattredd]

That's fair. Good call