Added DOMEditAction::toString(), not yet tested
Adds a test of DOMEditAction::toString() w/bug fixes
Completes DOMEditAction::toString() tests and bug fixes
Updated plan doc, improved some code comments
Draft of DOMEditAction::undo() and redo(), untested
Making DOMEditAction::toJSON() consistent w/Node

Node::toJSON() gives a JSONable object, not the JSON string itself.  So
now DOMEditAction::toJSON() does the same.  Unit tests updated
correspondingly.
Adds tests for undo/redo of appendChild actions
Adds tests, bug fix for undo/redo of insertBefore actions
Adds tests, big bug fix for undo/redo of normalization

Normalization data used to be flat, not including child/grandchild/etc.
information.  But normalization is a recursive process, so to undo it,
we need data about all descendants.  These changes fix that problem,
and test the fixes.
Updating plan, to-do list, and some doc comments
Undo/redo test for normalize now more thorough
Adds test for undo/redo of removeAttribute

Plus documentation typo fixes
Adds test for undo/redo of removeAttributeNode
Adds test, bug fix for undo/redo of removeChild
Adds test for undo/redo of replaceChild
Adds test for undo/redo of setAttribute
Adds test for undo/redo of setAttributeNode