added the notion of router hierarchy

Now all routers are automatically added to a list and enabled the use of this.navigate('../other_route') which then takes the parent route to execute navigae on. Not tested but this should also enable this.navigate('../../other/route')
Fix middle-click and meta+click (new tab) on <Link>. Fixes #83.
0.20.2
Add note about zuul tests for contributors.
Simplify arities of setPath/navigate(). Fixes #81.
0.20.3
Update CHANGELOG

added tests and fixed a bug
Merge branch 'parent_routers' of github.com:MarkNijhof/react-router-component into parent_routers