[added] <Redirect/> component

closes #159
[added] support for extra props in Links, fixes #170
updated Link docs to include the mention of aditional props
path as initial prop of <Routes> for server render

issue #57
This allow for this.props.path to be passed to <Routes> on the server.

Also server side componentWillMount registers callbacks for each route
without removing as componentDidMount and componentDidUnmout won’t run
in server side.

Include is Router.renderRoutesToString for non async