Separate snippet invocation from jQuery traversal.
Metamucil.

Adding fiber. Yuk yuk yuk.
Refactor vain.render to be callback-first.

The template engine I first modeled vain against was blocking-first,
wherein if you provided a callback it resulted in the function doing a
blocking call of itself, then invoked the callback with the result. The
render method is now callback first. If you don't provide a callback
function it will use a Future provided by fibers to return the result
you requested.
snippetsToInvoke -> snippetsDiscovered
We may just have to require async.
Remove fibers.
Process snippets in render using events.
Refactor readFile to work asynchronously.
Don't evaluate express inside renderFile.

Turns out that takes a bit (~ 90ms) and mocha doesn't like it. Let's do
it at the top.
Reduce number of arguments passed into snippet functions.

The argument list for snippet functions was getting pretty gnarly, so
we're making some changes. Specifically,

- The request and response are now passed into the params object, so you
  can't use those names for params passed in from markup.
- The current element is bound to this so it doesn't need to have its
  own argument.
Update tests for new snippet argument list.
Update README with new new on snippet strcutre.
Merge pull request #11 from farmdawgnation/call-me-maybe

Snippets can now handle asynchronous operations.