* Add anchor existant checking to link_checker component

* Oops, forgot some changes

* Drop scraper dependency and rework tests

* Handle name attributes

As mentioned in #381, crates.io 404's any request without an Accept:
text/html header.  It 200's any request with one, but at least
false-successes don't prevent checking any other links.

This also makes it easier to add a custom User-Agent if desired.

rustfmt and fix a clippy nit (unnecessary return) while I'm here.

Close #115