Update SSL support a bit.

Update SSL support a bit.

Use cmake's FindOpenSSL.  Actually use the library definitions that
come out of it.  Also use the include path.  If SSL is disabled,
then build without any of this.  The result will be a version
of civetweb that includes openssl support using dlopen() - ie,
what we used to do.  This is probably a bit silly, and I hope
nobody actually expects to use it that way, but it's mostly harmless.

Signed-off-by: Marcus Watts <mwatts@redhat.com>