gen-art-13+14+15+17+18

[petithug]

• "a node constructs" -> "a node MUST construct".
• "resulting message will use the normal overlay routing" -> "resulting message MUST use the normal overlay routing".
• "The node can also" -> "The node MAY also".
• "Because messages> may" -> "Because messages can".
• "the request is retransmitted" -> "the request MUST be retransmitted".

Bug: deanwillis/p2psip-base-master#149 Bug: deanwillis/p2psip-base-master#150 Bug: deanwillis/p2psip-base-master#151 Bug: deanwillis/p2psip-base-master#153 Bug: deanwillis/p2psip-base-master#154