[Rust] rsv crate with serde support

[mostlymaxi]

Decided to just go ahead and make an rsv encoder/decoder using the serde framework for rust. Should make it compatible with most structs and types (w.i.p) that have Serialize/Deserialize traits.

Probably a bit too big to shove into this challenge but figured I'd link it in case someone else wants to play around with the crate.

[simonrupf]

And based on the above library, I could add RSV support to convert2json, so we can now convert it to JSON and query it in jq:

$ rq .[0][1] Valid_001.rsv
"🌎"
$ rsv2json Valid_001.rsv
[["Hello","🌎",null,""],["A\u0000B\nC","Test 𝄞"],[],[""]]