Fixes #1 and #9, and adds #7 and #8

- Added support for specifying multiple URLs to crawl (start in config.yml can now be a single value or an array)
- When a page has a status code other than 200, it displays a Page not indexed notification
- URL matching fixed to allow correct subdomains on links in this format: /this/is/a/link
- Fixed bug where the same broken links were attempted over and over due to lack of marking them as traversed
- Optimized various code internally