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.

coins/monero/src/lib.rs

@@ -1,3 +1,17 @@
+///! monero-serai: A modern Monero transaction library intended for usage in wallets. It prides
+///! itself on accuracy, correctness, and removing common pit falls developers may face.
+///!
+///! monero-serai contains safety features, such as first-class acknowledgement of the burning bug,
+///! yet also a high level API around creating transactions. monero-serai also offers a FROST-based
+///! multisig, which is orders of magnitude more performant than Monero's.
+///!
+///! monero-serai was written for Serai, a decentralized exchange aiming to support Monero.
+///! Despite this, monero-serai is intended to be a widely usable library, accurate to Monero.
+///! monero-serai guarantees the functionality needed for Serai, yet will not deprive functionality
+///! from other users, and may potentially leave Serai's umbrella at some point.
+///!
+///! Various legacy transaction formats are not currently implemented, yet monero-serai is still
+///! increasing its support for various transaction types.
 use lazy_static::lazy_static;
 use rand_core::{RngCore, CryptoRng};
 
@@ -14,7 +28,7 @@ use curve25519_dalek::{
 pub use monero_generators::H;
 
 #[cfg(feature = "multisig")]
-pub mod frost;
+pub(crate) mod frost;
 
 mod serialize;
 
@@ -29,6 +43,8 @@ pub mod wallet;
 #[cfg(test)]
 mod tests;
 
+/// Monero protocol version. v15 is omitted as v15 was simply v14 and v16 being active at the same
+/// time, with regards to the transactions supported. Accordingly, v16 should be used during v15.
 #[derive(Clone, Copy, PartialEq, Eq, Debug, Zeroize)]
 #[allow(non_camel_case_types)]
 pub enum Protocol {
@@ -38,6 +54,7 @@ pub enum Protocol {
 }
 
 impl Protocol {
+  /// Amount of ring members under this protocol version.
   pub fn ring_len(&self) -> usize {
     match self {
       Protocol::Unsupported => panic!("Unsupported protocol version"),
@@ -46,6 +63,8 @@ impl Protocol {
     }
   }
 
+  /// Whether or not the specified version uses Bulletproofs or Bulletproofs+.
+  /// This method will likely be reworked when versions not using Bulletproofs at all are added.
   pub fn bp_plus(&self) -> bool {
     match self {
       Protocol::Unsupported => panic!("Unsupported protocol version"),
@@ -59,6 +78,7 @@ lazy_static! {
   static ref H_TABLE: EdwardsBasepointTable = EdwardsBasepointTable::create(&H);
 }
 
+/// Transparent structure representing a Pedersen commitment's contents.
 #[allow(non_snake_case)]
 #[derive(Clone, PartialEq, Eq, Debug, Zeroize, ZeroizeOnDrop)]
 pub struct Commitment {
@@ -67,6 +87,7 @@ pub struct Commitment {
 }
 
 impl Commitment {
+  /// The zero commitment, defined as a mask of 1 (as to not be the identity) and a 0 amount.
   pub fn zero() -> Commitment {
     Commitment { mask: Scalar::one(), amount: 0 }
   }
@@ -75,12 +96,13 @@ impl Commitment {
     Commitment { mask, amount }
   }
 
+  /// Calculate a Pedersen commitment, as a point, from the transparent structure.
   pub fn calculate(&self) -> EdwardsPoint {
     (&self.mask * &ED25519_BASEPOINT_TABLE) + (&Scalar::from(self.amount) * &*H_TABLE)
   }
 }
 
-// Allows using a modern rand as dalek's is notoriously dated
+/// Support generating a random scalar using a modern rand, as dalek's is notoriously dated.
 pub fn random_scalar<R: RngCore + CryptoRng>(rng: &mut R) -> Scalar {
   let mut r = [0; 64];
   rng.fill_bytes(&mut r);
@@ -95,6 +117,7 @@ pub fn hash(data: &[u8]) -> [u8; 32] {
   res
 }
 
+/// Hash the provided data to a scalar via keccak256(data) % l.
 pub fn hash_to_scalar(data: &[u8]) -> Scalar {
   let scalar = Scalar::from_bytes_mod_order(hash(data));
   // Monero will explicitly error in this case