Hints lookup table for explaining SSL errors

[aantron]

SSL errors are very cryptic, causing confusion in general experience and in #246 in particular. #259 and savonet/ocaml-ssl#108 should make this better by rearranging the SSL error output in Dream's logs. However, some of SSL's own error messages are still too brief and confusing, so it may be good for Dream to have a small table that contains additional hints to print to the log for certain errors.

For example, for the error in #246, Dream might print a warning like

WARN REQ 42 Hint: may be due to an plaintext HTTP request to a TLS server.

...or some even better phrasing explaining what is actually going, so the user is more likely to quickly figure out what is happening, especially if this is in development.