Update CHANGELOG for refactor

CHANGELOG.md

@@ -4,6 +4,12 @@ Change Log
 All notable changes to this project will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/).
 
+## [Unreleased]
+
+### Changed
+- Massive refactor of back-end code.  Inbucket should now be both easier and
+  more enjoyable to work on.
+
 ## [v1.3.1] - 2018-03-10
 
 ### Fixed

pkg/message/manager.go

@@ -45,7 +45,8 @@ func (s *StoreManager) Deliver(
 	prefix string,
 	source []byte,
 ) (string, error) {
-	// TODO enmime is too heavy for this step, only need header
+	// TODO enmime is too heavy for this step, only need header.
+	// Go's header parsing isn't good enough, so this is blocked on enmime issue #64.
 	env, err := enmime.ReadEnvelope(bytes.NewReader(source))
 	if err != nil {
 		return "", err