Ability to rename and reorder nodes, plus more

Some utility methods were added long the way.
Remove namespacing from Node tests (e.g., "SafetyPin::")
Rename Node#move to Node#move_within

It's more descriptive of what the method actually does — leaving it as move implies a similarity to the "mv" unix utility, which isn't exactly the case.
Add auto rename option to Node#move_within