Fix broken doc links and http→https where possible

Fix broken doc links and http→https where possible

I got a cookie-cutter email from folks noting the modssl.org doc links
were broken and asking us to use their site instead, which was both
helpful and a rather heavy page with advertising on it, so not something
I want our docs to link to.

Fixed the modssl link to point to the correct current Apache docs, since
mod_ssl has not been a separate project for … a very long time.

Audited every `http:` link in the Spec, replacing with https if
available, updating URLs as needed, or trimming deadwood as appropriate.
This did edit one license text, but in a way which I believe is
reasonable and in the license holder's best interests.

* Use comments with a datestamp for any remaining http: URLs, showing
  when they were last audited
* Suggest migrating away from Berkeley DB.
* Drop mention of a patched `pam_unix` module which is no longer available.
* In revamping the CDB tools links, add my own tools.
* Redo the intro text for the mod_ssl stuff (first person voice of PH).
* Rescorla's book's online examples appear to be gone; drop mention of
  them and point to Ristić's more recent book too.
* Point to wikipedia list of DNSxL services as an overview, in part
  because I dropped the reference to the defunct rfc-ignorant.org and
  there was no good candidate as an exemplar for domain-based lists.
* Note that mksd is a candidate for removal from Exim since mks_vir
  is dead.
* Drop LogReport/lire reference (dead/gone and can't find it).
* Redo proxy protocol spec-linking text.
* Replace FAQ A1701 with text saying "don't do that" (self-signed certs)
  and just telling people to use a CA instead, pointing strongly to
  Let's Encrypt.  We did nobody any favors with that old text still
  being present today (it was entirely appropriate when written).