6.1.0

CHANGES:

done by @psafont in #417:

• conduit-lwt-unix-ssl: allow users to create a client ssl_context and use it for
  any connections. This allows users to manage the lifecycle of the context.
• conduit-lwt-unix-ssl: domain name verification can be disabled by users,
  it's enabled by default. The library returns an error when the hostname
  verification is turned on but it cannot be performed, this follows the TLS
  implementation.
• conduit-lwt-unix-ssl: IP verification can be enabled by users, it's disabled
  by default.
• conduit-lwt-unix-ssl: SNI is not sent when there isn't a domain name available
• conduit-lwt-unix: avoid direct use of Ssl in conduit_lwt_unix (#418 @psafont)