Implement custom tls options

This allows users of the API to either specify a simple CA-File for
certificate verification, or a custom SSLContext in order for a more
fine-grained control of the TLS options they want to use.

As of now, no additional tests were added, but the existing tests were
changed to reflect the changes in internal methods, so that they can
still pass
Modify parameters to reflect set_params hash

By default, we don't set any parameters (empty or no :tls_options). If
the hash is non-empty, we pass it directly to set_params and use the
resulting context for creating the TLS socket.
Add comment for TLS verification in 1.0 release
Merge pull request #161 from sonOfRa/tlsoptions

Implement custom tls options