- Remove appropriate route change subcriptions when a root is removed
via `m.mount(root, null)`.
- Don't pollute `onpopstate` and friends - use standard event listeners
instead.
- Simplify and streamline subscriptions, in preparation of adding a
`remove` parameter to `m.mount`.
- Change the redraw internals to redraw immediately, with ability to
cancel via returning a sentinel.
- Change `"bleeding-edge"` for `m.version` in `next` to instead just be
the latest `m.version`. (If you're using `next`, you should know what
you're in for.)
- Update tests to be aware of these changes. (Some were failing for
subtle reasons.)
- Drive-by: remove some uses of `string.charAt(n)` and use `string[n]`
instead.
