[RAW] swim: introduce failure detection component

Failure detection components allows to find which
members are already dead.

Public API:

swim.cfg({server = <uri>, members = <array of uris>,
          heartbeat = <seconds>})

    Configures the SWIM module.

    @server - URI of UDP server to which other cluster
        members will send SWIM messages. It should
        have the format "ip:port".

    @members - array of URIs explicitly defined by a
        user. These members are never deleted from
        members table until they are removed from the
        configuration explicitly. SWIM downloads from
        them their members tables, merges with its
        own and repeats.

    @Heartbeat - how often send a part of members
        table to another member. Note, that it is not
        how ofter send the whole table, nor how ofter
        to send the table to all members. It is only
        one step of the protocol.

swim.stop()

    Stops the SWIM module: shuts down the server,
    closes socket, destroys queues, frees memory.
    Note that after it swim.cfg can be called again.

swim.info()

    Show info about each known member in the format:
    {
        ["ip:port"] = {
            status = <alive/dead>,
            incarnation = <growing unsigned number>
        }
    }

Closes #3234