eslint cleanup; trailing comma fix for IE

- Removed unused variables
- Removed double declarations
- Most importantly, removed trailing commas which were breaking IE
- Added eslint.json for future eslint usage
Preserve unused function arguments
Merge pull request #122 from aaronshaf/eslint-cleanup

eslint cleanup; trailing comma fix for IE
[added] animation example

abused the [added] flag just for marketing in the
changelog cause THIS IS EPICLY AWESOME

closes #17
typo
release v0.4.2
manual changelog update

poor CONTRIBUTING.md, all alone with nobody
reading it…
[changed] Split <Routes> component from <Route>

Fixes #112.

Test Plan: Loaded each of the examples and clicked
around. npm test too.
release v0.5.0
[fixed] middle click on <Link/>

Restore the de facto browser behavior for middle
click on links: Open to background tab.

closes #120
[fixed] alt click on Link should count as modified
[changed] make URLStore.push idempotent

If somebody’s component is observing some user
input its easy to start pushing the same url
into the store, this makes it so devs can kind
of treat `Router.transitionTo` like rendering,
nothing happens if nothing has changed.

Previously, you get a bunch of history entries
that don’t change UI as the user clicks the back
button.

closes #79
Merge pull request #124 from spicyj/altkey

[fixed] alt click on Link should count as modified
[added] Router.AsyncState mixin

Helps with #57