## Thoughts

  * ~~strip hashes and everything following (as they're in-page anchors)~~
  * strip args
  * ~~use `pop()` on the set instead of `.remove()`~~
    * ~~return false once the set is empty~~
  * ~~`WebPage.parse_urls()` needs to compare startswith to base url~~
  * ignore any links which aren't to pages
  * better url checking to get bare domain
  * remove base url from initial urls with and without trailing slash