Better resolving of hyperlinks

[dteviot]

Multiple issues.

1. Detection of next/previous chapter is foiled by HTTP redirection, where page is at different URL to that requested. Note, should be able to track this by examining xhr's 'url' property in Parser.fetchChapter().
2. What to do with hyperlinks? Remove or just convert to text? Note, sometimes want to keep because they're footnote links. (Note, difficult to deal with if go to another page, because don't know the URL that will be assigned to the page in EPUB.)