migrate `inflate` method to accept `Node` objects

Previously, `Node` was the only type, so one was created
automatically. Now, the user-supplied inflate methods emits Node
objects (or subclasses of).
rename 'createClass' to 'extend'; add tests

Nodes can be subclassed. Basic tests pass.
reimplement `Node.extend` on Backbone's internal extend; remove cruft

The cruft was lingering references to `Node.clone`, which needed to
instead reference the current (dynamic) node subclass (if any).

Backbone's `extend` implementation fit very well for my Node subclass
needs, and it needed little modification. I am considering replacing
the `__super__` reference with a reference to the parent constructor
instead of the contructor prototype. Seems more useful. Not urgent.
implement `_tree.Tree.extend`; refactor `new Tree` to accomodate

`Tree` can now be extended in the same way as `Node`. I'm not at my
best right now, and think that I might not have implemented it
correctly in all cases. `_tree.fromNode` was a picky instance, where
the new tree could reasonably be an instance of the node's original
tree's class, or an instance of the passed-in default tree class. I
went with the default option , since `fromNode` should not assume the
new tree will necessarily be like the previous.
test exposed Tree.clone method against custom classes
reimplement TodoList as treeClass instead of mixins

I don't even think mixins are necessary anymore. The one thing on my
mind I've yet to try is dynamically adding nodes of different
subclasses. I think it should work already.

But yeah, mixins may stick around or be deprecated (leaning towards
deprecation). I much prefer the `.extend` way. I'll first reproduce
all mixin tests using `.extend`, compare the code, and decide wheter
mixins still have value.
API updates; jshint fixes; serialize in TodoMVC example

Subclass stuff has been added to the README.

`serialize` was implemented naively for the TodoMVC example, to
support data model persistence. Works ok.

trailing whitespace. capitalized constructors. yadda yadda.
jshint fixes
fix README wiki links

Used parens instead of braces.
Uphold licensing requirements for backbone

The  implementation was largely backbone's. Much thanks.
test subclass behavior for `parseAndAddChild` and `addChildNode`

To round out the `Node`/`Tree` subclass implementation, these tests
ensure that dynamically added nodes behave as expected with custom
subclasses.
removed quotes; they weren't necessary
remove quote link on ToC
remove h1, unnecessary
move API higher on the README page
v0.6.0: `Node` and `Tree` subclass for modeling

Mixins were the first attempts at customizing `_tree`'s behavior for
application-specific data modeling. Subclassing solves roughly the
same set of problems, and does so in a cleaner (opinion) way. Mixins
may be deprecated in the future.