Added whitelistUrls, inverse of ignoreUrls

As discussed on Twitter, this enables us to restrict errors to be just our own code, rather than other errors from extensions, third party scripts, etc.

Tweets: https://twitter.com/miksago/status/335434428543283200, https://twitter.com/mattrobenolt/status/335446234254938112, and https://twitter.com/mattrobenolt/status/335491751571775489


Also added documentation for format of documentation.. (if you want, I can remove this)