Fixed SSL_recv_char and added certificate validation

I've fixed an issue in which SSL_recv_char returned garbage instead of throwing an EoF. I've also added ssl certificate validation which can be disabled by adding "-D hxssl_no_cert_validation" as a compiler flag. Default file and folder are /etc/ssl/certs/ca-bundle.crt and /etc/ssl/certs respectively, but this can be changed by passing in custom file/folder arguments to the setCertificateLocations() method on neko.tls.Socket.