In order to better support redirection, we should replace the redirection API with onEnter and onExit.

The onEnter function is called when the new location results in a RouteMatch that was not previously present on RouteMatchList:

matchList = [ "/a"]
matchList' = [ "/a", "b"]

When matchList changes to matchList', the onEnter callback for Route "b" will be called, and the callback for "/a" will not.

The onExit callback is invoked when the reverse is true:

matchList = [ "/a", "b"]
matchList' = [ "/a"]

When matchList changes to matchList', the onExit callback for Route "b" will be called.