Release v2.3.1

• Bugfix: Handle another strange date I have come across in my sample data.

Release v2.3.0

• On header.ErrManyFields failure, (*header.Header).Get() now returns the value of the first field found with the error.
• Add a header.ParseTime() function which provides the same time parsing facilities that (*header.Header).GetTime() and (*header.Header).GetDate() use.
• Add a header.ParseAddressList()function which provides the same addr.AddressList parsing facilities that are built in to the various address parsing methods of header.Header.

Release v2.2.1

• Bugfix: Fixed a typo in header.ErrNoSuchField error message.

Release v2.2.0

• Deprecation: The contents of the walker package are deprecated and will be
  removed in a future release. Use the features of the walk package instead.
• Add the walk package.
• Add walk.AndProcess and walk.Processor to handle walking a message part tree
  with the goal of generic message processing.
• Add walk.AndTransform and walk.Transformer to handle walking a message part
  tree, which is a process tool that aids with message transformation.
• Add walk.AndProcessSingle to process single parts of a message.
• Add walk.AndProcessMultipart to process multipart parts of a message.
• Add message.NewBuffer to copy message.Part into a message.Buffer.
• Add message.NewBlankBuffer to copy message.Part into a message.Buffer, but
  without body content or sub-parts.
• Add (*message.Buffer).AddBuffers method for convenience.

Release v2.1.0

• Deprecation: The OpaqueAlreadyEncoded() method should no longer be used.
  Instead, call SetEncoded(true) on a mesage.Buffer and then call Opaque() to
  achive the same result.
• Calls to message.Buffer's Opaque() and Multipart() methods are now guaranteed
  to work if called repeatedly.
• Add the Buffer.SetMultipart method for setting the message.BufferMode
  of a message.Buffer to message.ModeMultipart and setting the capacity of the
  internal parts slice.
• It is now possible to use message.Buffer as a message.Part directly.
• Add the Buffer.SetOpaque method for setting the message.BufferMode of a
  message.Buffer to message.ModeOpaque.
• Add a linter to check changelog correctness.
• Add a linter to check for bad patterns in golang.
• Add tools to manage the release process.