Improved typescript support

[GianlucaGuarini]

This PR is a breaking change and adds the withTypes method in order to get a better typescript support to Riot.js components.

The new method allows us writing components as follows:

<my-component>
  <p>{ state.greeting }{ props.username }</p>

  <!--
    Notice that lang="ts" does actually nothing.
    It's just needed to let your IDE interpret the below code as typescript.
    The riot compiler will ignore it
  -->
  <script lang="ts">
    import {withTypes, RiotComponent} from 'riot'

    export type MyComponentProps = {
      username: string
    }

    export type MyComponentState = {
      message: string
    }

    export type MyComponent = RiotComponent<MyComponentProps, MyComponentState>

    export default withTypes<MyComponent>({
      state: {
        message: 'hello'
      }
    })
  </script>
</my-component>

This is a breaking change that requires a new RIot and Compiler release.

[kachurun]

I love you dude, I crutched it in my project three days ago. Now this is not needed and everything will work natively. Perfect!