Add Composer support

[RobLoach]

Composer is a package manager for PHP. This allows HTML5 Shiv to be downloaded by putting "afarkas/html5shiv" into your own composer.json file.

{
  "require": {
    "afarkas/html5shiv": "3.6.*"
  }
}

[sgrodzicki]

👍

[thomaswelton]

I came here to check to see if there were any existing open pull requests for adding a bower.json file for package management using bower.

I also use Composer, on my PHP projects but I'd recommend using bower for installing javascript and front end dependencies.
I've been using bower to install this repo for a while. However I'm going to submit a pull request to make bower integration a little better by specifying the main export files.

[sgrodzicki]

@aFarkas please merge!

[RobLoach]

Thanks a lot for the help. Added to Packagist:
http://packagist.org/packages/afarkas/html5shiv

Feel free to create a username and post it in a comment here, and I'd gladly add anyone as a maintainer of the package there.