Reduce indentation level by 4,
add code documentation,
remain under 120 chars wide.

update license notice (2017)

msvc: change contrib repo sources

The op token is renewed regularly (around every 30 minutes),
so SHA256 provides enough security for this non-sensitive token.
SHA256 takes 32 bytes instead of 64 bytes for SHA512,
and the token is included in every listen requests,
renewed every 30 seconds, and every answer to get.
In the context of limited bandwith usage, using SHA256 seems more appropriate.
This change is backward and forward compatible.

Clear the search node acked when clearing
the corresponding announce, after checking
the announce status for all announces.

routing_table: complete connecting state resolution

After a connectivity change, the DHT would enter the "connecting" state in order
to try to resolve good nodes. However, the previous algorithm would
probabilistically increase time for completion each time a node would fail to
resolve. We now avoid this by prioritizing non-expired nodes in the process.
Also, a subtle error would sensibly stop the process for 30 minutes due to using
the Node::NODE_EXPIRE_TIME constant instead of Node::MAX_RESPONSE_TIME.

remove InfoHash::toCString()

Implementation of InfoHash::toCString() is broken