Added support for DOMContentLoaded

## 1. DOMContentLoaded
Basically supported in all browsers, except IE < 9. While jQuery does offer it's own document.ready functionality, which is support all the way back to IE6, I do not consider this a polyfill, since it most likely fires at a later time (either readystatechange or polling with the scroll hack, [read more](https://github.com/dperini/ContentLoaded/blob/master/src/contentloaded.js)).

## 2. validate script can now run from every cwd
Also hardened the `validate-jsons.js` script a bit more, you can now run node from any directory, and it will still work :)
```bash
cd ~
node projects/caniuse/validator/validate-jsons.js
```
```bash
cd ~/projects/caniuse/
node validator/validate-jsons.js
```
```bash
cd ~/projects/caniuse/validator/
node validate-jsons.js
```