Add custom exception SslHandshakeError

[dencrypt-jacob]

@lganzzzo
I have added a custom exception for SSL handshake errors. The mbedtls error code from mbedtls_ssl_handshake is part of that and can be inspected by the client.

[dencrypt-jacob]

Ping @lganzzzo

[lganzzzo]

Hello @dencrypt-jacob ,

Thanks for the PR, and sorry for the late reply.

This is a good proposition, however, it can't be merged right away as it will cause crash (because of the throw) in current implementations of connection handlers and in HttpProcessor::Task::run.

Thats why I'm still waiting merging it.
Until I come up with the idea how to handle it better (most probably it will be just catch ignoting the error)