message: Improve docs for key_prefix, multi_key_prefix
diff: @@ -14,7 +14,8 @@ fn len(prefix: &[u8]) -> [u8; 2] {
  [length_bytes[6], length_bytes[7]]
  }
  -// prepend length of the namespace
  +// Calculates the raw key prefix for a given namespace
  +// as documented in https://github.com/webmaster128/key-namespacing#length-prefixed-keys
  fn key_prefix(namespace: &[u8]) -> Vec<u8> {
  let mut out = Vec::with_capacity(namespace.len() + 2);
  out.extend_from_slice(&len(namespace));
  @@ -22,6 +23,8 @@ fn key_prefix(namespace: &[u8]) -> Vec<u8> {
  out
  }
  +// Calculates the raw key prefix for a given nested namespace
  +// as documented in https://github.com/webmaster128/key-namespacing#nesting
  fn multi_key_prefix(namespaces: &[&[u8]]) -> Vec<u8> {
  let mut size = namespaces.len();
  for &namespace in namespaces {
  