Small refactor including multiple handlers and paramification

Including slightly improved readme. Improved lib, added better
comments. Added LICENSE. Slight change to .gitignore.

Below are the changes from the other branches.

Support for multiple handlers

Added three tests for this. This allows us to have `route.get(path,
fn1, fn2,
fnN)` but only the last handler, `fnN` will receive the next generator.
This is very useful for adding little permission checks or something
similar to your routes, they can then throw to disrupt the middleware.

Also removed soft dependency on the koa repo in favor for * from npm.

Added support for paramification

This is inspired by koa-params, but I want it in the router, not as a
hard shell around it as that means most new features in the router
won’t be available once params has taken over.

This allows for `route.param(name, fn*)`. The `fn*` receives the
context and can perform some neat stuff like retrieving resources based
on ids in the path. These functions I call paramifiers and they are
yielded before any route handlers. They can throw if somethings wrong,
for example 404 if a resource is missing.