Adding some better docs

src/lib.rs

@@ -47,13 +47,24 @@ mod serial;
 use std::fmt;
 
 /// The type of key that should be created
+/// 
+/// Each key variant has a number value attached to it which
+/// represents the length of the key it represents.
 #[derive(Clone, Serialize, Deserialize, PartialEq, Eq, Debug)]
 #[repr(u32)]
 pub enum KeyType {
-    Aes128,
-    Aes256,
+    Aes128 = 32,
+    Aes256 = 64,
 }
 
+/// A crytographic key
+/// 
+/// Uses a `union` to allow key inlining without heap allocation.
+/// Provides easy to use constructors for generation and derivation
+/// from user input/name.
+/// 
+/// Also implements `serde::{Serialize, Deserialize}` via a custom
+/// serialiser which allows easy encryption of the key itself.
 pub struct Key {
     tt: KeyType,
     key: KeyBuf,