* add TCP StatsD listener support
* add listen-tcp flag to control UDP/TCP mode on same port
* statsdListenUDP/statsdListenTCP as string, and alias listen-address to listen-udp
* add stats for tcp error/line_too_long
* add test for TCP listener
Instead now we will send a warning message to the logs
and continue on with our day.
Also a guard has been added when we detect a channel has been
closed and the `Exporter.Listen` function will return out of
its loop vs always running. When a channel is closed there will
be no more data to consume, so this seems correct. It also allows
for a test to be written for the panic.
