3.15.0

CHANGES:

• Update unikernels (@hannesm, #621)
• Extend the Smart protocol with have and want (@plangesd, @dinosaure, #626)
• Rename function to get capabilities from the client and the server (@Julow, #627)
• Extend the Smart protocol with a possible done or a flush (@plangesd, #628)
• Extend the Smart protocol with ack and handle empty request (@plangesd, @Julow, #629)
• Add missing new lines for the server side (@plangesd, #630)
• Be more cooperative with other services (like http) when we clone (@dinosaure, @hannesm, #631)