Helper to retrieve CRL URIs from a certificate

[bdewater]

Similar to #260

According to RFC 5280 a distribution point can contain a lot of things, but in practice I'm seeing only fullName URIs (6).

[ioquatix]

Do you think we should add an example showing how to use it/why to use it?

[bdewater]

I guess https://github.com/ruby/openssl/blob/master/sample/crlstore.rb could be updated, but that one in itself isn't terribly clear either 😕

I was planning to use it myself in cedarcode/webauthn-ruby#208 where I currently have a more brittle and uglier regex match to get the URI.

[ioquatix]

For the name of the module, what are your thoughts on the casing, should it be CRLDistributionPoints since CRL is an abbreviation?

[bdewater]

Sounds good to me, updated.

[bdewater]

Hum, one flaky test that failed (and I can't restart) but the rest is all green.

Edit: fixed with a rebase on top of #278

[ioquatix]

LGTM.