Deleted guff.
Rewrote comic crawlers to use treeFetch.

Created the type LinearComic, which contains
all the necessary information about a linearly structured webcomic (i.e.
one image per URL and next/previous-links to follow).

The comics are now in Comic.List. A comic can now be downloaded with
LinearComic.getLinearComic and .getLinearComicBack. The first downloads
from oldest to newest, the second from newest to oldest.