Type improvements (#706)

* use nanobus for the emitter typings

instead of `events`, which is a bit different

* add typings for `cache` option

index.test-d.ts

@@ -0,0 +1,40 @@
+import { expectAssignable, expectType } from 'tsd'
+import Choo = require('.')
+
+new Choo({})
+new Choo()
+
+new Choo({ cache: 100 })
+new Choo({
+  cache: new Map()
+})
+new Choo({
+  cache: {
+    get: (id) => null,
+    set: (id, value) => expectType<any>(value)
+  }
+})
+
+const app = new Choo({
+  history: false,
+  href: true,
+})
+
+app.use((state, emitter) => {
+  state.title = 'choo choo'
+  emitter.on(state.events.DOMCONTENTLOADED, () => {
+    emitter.emit('example')
+  })
+})
+
+app.route('/', (state, emit) => {
+  expectAssignable<object>(state.params)
+  expectType<string>(state.href)
+  expectType<string>(state.route)
+  expectType<string>(state.title)
+  emit('example')
+})
+
+expectType<string>(app.toString('/'))
+
+app.mount('body')