Validate options

[asbjornu]

If you, for instance, pass assume_extension: true to HTMLProofer now, it is going to fail with the following error:

NoMethodError: undefined method `empty?' for true:TrueClass
    ./lib/html_proofer/attribute/url.rb:138:in `file_path'
    ./lib/html_proofer/utils.rb:12:in `blank?'
    ./lib/html_proofer/attribute/url.rb:128:in `absolute_path'
    ./lib/html_proofer/check/links.rb:57:in `block in run'

This error is a bit hard to decipher since it is not pointed to the fact that the problem stems from an invalid type being passed in options and it also doesn't say which option key is problematic. This PR adds validation of options on initialization so more user-friendly and descriptive errors are thrown when options have invalid values.

[asbjornu]

This does not feel like an elegant or bullet-proof way to enumerate all existing options to extract their default value type. Suggestions for how to improve this would be appreciated.

[asbjornu]

I can see that I've managed to add the file spec/html-proofer/fixtures/links/erstiebegrüßung.html in this PR. I have major issues with that file on macOS 11.7. I've attempted to do everything mentioned in this post, but the file is still deleted and re-added at random and makes other Git operations such as rebase, impossible.

[asbjornu]

As #772 is merged, this PR has now been rebased on HEAD of main, the file erstiebegrüßung.html is gone, and the PR should be ready for review.

[gjtorikian]

Thanks! I'm going to release this as a 4.x bug fix for this and then work more on V5 (#759) this weekend.

[Mihail211292]

options.is_a?(Hash)+ ({yes}))