This method constructs a Certificate instance from a server,

containing the hostname, port, and certificate data. This can be used

to retrieve state from a certificate when encountering an SSL error,

which does not itself represent certificate information.
No validation on the certificate itself will be performed (aside from

attempting to load the content). It's the caller's responsibility to

process the certificate in whichever way it needs.

Unit tests pass.
Used this in the upcoming SSL error class work.