doc: add documentation for errors

This adds documentation around what errors are generated by Node and how to intercept them.

The rendered docs are available [here](http://neversaw.us/nodejs-api/errors.html).
This API is outlined in a previous link. It is V8 specific and I don't believe it should be included here. Additionally, a parameter is missing:
```
Error.captureStackTrace(targetObject[, callingFunction])
```