Ability to disable SSL session verification

See also:

https://github.com/ncr/rack-proxy/issues/16
Ability to set SSL_VERIFY_NONE option for instance

This means **all** requests going through the `Rack::Proxy` instance
will disable SSL session verification.
Merge pull request #28 from simplybusiness/disable_ssl_session_verification

Ability to disable SSL session verification
Bump