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.

crypto/multiexp/Cargo.toml

@@ -8,6 +8,9 @@ authors = ["Luke Parker <lukeparker5132@gmail.com>"]
 keywords = ["multiexp", "ff", "group"]
 edition = "2021"
 
+[package.metadata.docs.rs]
+all-features = true
+
 [dependencies]
 zeroize = { version = "1.3", features = ["zeroize_derive"] }