Introduce an OpenSSL::Crypto backend for the hashes library
and an OpenSSL::SSL backend for the TLS support in our https
method.

Many thanks to curl for showing the way with how to handle
a CRL file. There are some memory leaks here with the
TlsFd itself as well as the proxy support; and we should
reorganize the code to generate the ssl object as late
as possible.

A peculiar aspect of OpenSSL is that SSL_has_pending() returns
1 even if SSL_read() will fail to read anything and return the
equivalent of EAGAIN. We work around this here by also peeking
ahead 1 byte. I was running a very high RTT connection from
Germany to Australia for testing, and with the peeking it's
using negligible amounts of CPU; before that, it was busy
looping at 100%. Bad OpenSSL!