Initial documentation for the Monero libraries (#122)

* Document all features

* Largely document the Monero libraries

Relevant to https://github.com/serai-dex/serai/issues/103 and likely 
sufficient to get this removed from 
https://github.com/serai-dex/serai/issues/102.

contracts/extension/Cargo.toml

@@ -5,6 +5,7 @@ description = "An ink! extension for exposing Serai to ink"
 license = "AGPL-3.0-only"
 authors = ["Luke Parker <lukeparker5132@gmail.com>"]
 edition = "2021"
+publish = false
 
 [dependencies]
 scale = { package = "parity-scale-codec", version = "3", default-features = false, features = ["derive"] }