duplex mode with ratio

[untoreh]

• deprecate lassos
• use flings for inbound data
• the fling server should manage this
• cli should offer option for both tx/rx payloads sizes

[untoreh]

since no data is transferred before the connection close, the ends don't know when each one has finished writing.
So some time sync with timeouts should take place to reduce overhead of eventual reflings

[untoreh]

Because data is not sent until the connection is closed, this must use TCPConn instead of Conn to use ReadClose and WriteClose directly.

[untoreh]

duplex mode is configurable so that can be enable on both fling and lassoes or only one of them or none at all.
no duplex seems to help push more bandwith

[untoreh]

duplex makes only sense for flings because when a fling is handled it is sure the read follows so that something can be wrote back, while lassoes normally wait to be written so can't be trusted to be read right away

[untoreh]

add information about queue of waiting incoming shots from remote to allow client to dial more conns when needed