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).
Drop the usage of dashes. Technical documentation should be more straight forward. End the sentence or place the additional information in parentheses if it adds clarification. e.g.

> Note that the stacktrace string is generated on **access (i.e. it is lazily generated).