navlink performance improvement, provide createNavLink, remove handleRoutes

[kaesonho]

Higher order component pattern is good but since users might use NavLink everywhere, so having connectToStore -> handleRoute -> NavLink -> a should be too much and the performance might be able to be improved.

1. We only use makePath and isActive from routeStore, use it directly, so that we can reduce two higher component and we can remove the eventListeners to the RouteStore. previously the RouteStore might propagate hundreds emitChange to every NavLink on the page.
2. move out NavLink functions to be navLinkUtils, so that if users have the use case they can compose there own NavLink. provide createNavLink so that users can overwrite the attribute with whatever they want, maybe add a mixin or a custom click event handler

@mridgway @redonkulus @lingyan @Vijar

[kaesonho]

updated, now provide a function for users to overwrite attributes and create a NavLink component

[kaesonho]

updated, still listen to the RouteStore change.

[yahoocla]

CLA is valid!

[mridgway]

lgtm

[kaesonho]

thanks :fireworks:, squashed

[redonkulus]

:+1:

[kaesonho]

do we want to put createNavLink in lib ? or addons ?

[mridgway]

Keep it in lib since it's used by core. We can export it from require('fluxible-router').createNavLinkComponent.

[kaesonho]

updated, change file name as createNavLinkComponent, also export it with index.js

[lingyan]

:+1:

[mridgway]

:boat:

[kaesonho]

rebased, let me merge it

[roderickhsiao]

:+1: