frint-router-react: inline rendering via Route component

[fahad19]

Closes #302

Note: No breaking changes.

What's done

The <Route /> component now supports inline rendering via render prop:

<Route
  path="/about"
  render={() => <p>Hi</p>}
/>

Doing so would allow passing extra props to the components, without risking any unmounting of the rendered components:

import Foo from './Foo';
const fooProps = {};

<Route
  path="/foo"
  render={(routeProps) => (
    <Foo 
      customProps={fooProps} 
      {...routeProps} 
    />
  )}
/>

[coveralls]

Coverage increased (+0.02%) to 97.224% when pulling 1031478 on route-render into 416bc35 on master.