- consider creating YouTubeException to raise on failures rather than just
  a string so that we can pass our request params back up to higher
  levels should they be interested.

- look into object types stored for comments and channel list and see if
  we're doing the Right/Best Thing.  It looks like we've got hashes with
  one key e.g. "comments" that then map to a list of actual comments.

- add unit tests for client.videos_by_tag page and per_page params.

- add unit tests for specifying alternate api host/path in client
  constructor.
