Go implementation of the JWZ email threading algorithm (library)

 This package provides the original JWZ algorithm to implementors of
 the 'Threadable interface'. It has been tested against many thousands
 of emails.
 .
 Along with providing the threading capability itself, the package
 also provides:
 .
 + A generic walker, to which you can provide a function to operate upon
   the nodes in the threaded tree.
 + A generic sorter, to which you can provide your own comparison
   function (a byDate example is provided)