Turn Instantclick into a module if it needs to be one

[DecentM]

A lot of web developers use RequireJs, Browserify or the like, so this PR enables Instantclick to be require-d or import-ed from Javascript and Typescript entry points.

Regular functionality is the same. If the script runs plainly in the browser, it will attach the InstantClick object to window as usual.

I also added a package.json to let people do npm install https://github.com/dieulot/instantclick and be on their way.

I wrote the version number as 4.0.0, so that probably needs to be changed before merging into master.

[rstacruz]

Really would love this. I've been using @egoist's fork (https://github.com/egoist/instantclick) just so I can use instantclick without bower.