Make it possible to use IndexedDBShim directly with NPM through browserify

This fix doesn't break anything and actually fix the `main` attribute of the `package.json` file which presently points to a non-existing file.

And it makes it possible to use `IndexedDBShim` through NPM simply by doing:

    $ npm install git://github.com/axemclion/IndexedDBShim.git#commit-ish

And if you feel like it, you could even publish this module on NPM registry. That would be even easier for your users:

    $ npm install indexeddbshim

I have preferred to use an all-lower-case package name because this is the common best practice for module names. 

For the record, how to use browserify is described in details in https://github.com/substack/browserify-handbook

After those modifications there might still be things to tweak to improve the experience with NPM but that's the main starting point.

Cheers and I hope you will accept it