Add support for ignoring every URL on a page

[s-i-v-e]

We save our outdated pages in an archive folder.
These pages shouldn't be checked for broken links.
And to make this possible I adapted the script to avoid validating the URLs on the given list of markdown pages in a similar way as ignore_urls.

The option is

ignore_pages:
  - path/to/file
  - path/to/folder/*

It checks for every link if it is on a page that should be ignored.
Maybe it's possible that it checks the page before going through every URL on that page.

[mflehmig]

Hello, is there anyone looking into this MR? It looks very promising :-)