Adds CommonJS Compliance + package.json

Hi,
I just added a few lines of code as well as package.json, because:

* Hasher is now [UMD compliant](https://github.com/umdjs/umd/blob/master/returnExportsGlobal.js) and therefore can be used standalone, within a AMD environment _AND_ a CommonJS environment.
* Hasher can be published to NPM for the greater good
* I needed those modifications :smirk: 

Why I needed those may shed some light on why I pull-request:

I'm currently working on a browserify-based CommonJS-only client-side architecture, and I needed Hasher badly! But until I added the CommonJS compliance, I couldn't use it.

Moreover, I had to 

````
require('vendor/haser/dist/hasher.min');
````

which I find not very pretty, and adding `package.json` allowed me to beautifully replace the line above with


````
require('hasher');
````

What do you think ?

Cheers!