Remove a leftover debugging print
Don't allow WikiWords to occur in the middle of an email address
Remove the separation of _body and _children in ASTNode
Add a new TaggedNode class, and remove tag from ASTNode.

For thousands of years, Man has been crying out against the
folly---nay, the injustice!---of including a tag in the ASTNode
type. Some nodes, like Plaintext and Raw, have no tags, so clearly the
abstraction wasn't quite right.

 - Add a new TaggedNode type
 - Remove the tag and CSS class from ASTNode
 - Make almost everything extend TaggedNode now
 - Remove ContainerNode