Adds logplex_msg_buffer:lost/1.

Gets the number of messages noted as lost by the buffer.
Whitespace fixup.
Replace message_routed stat with drain_delivered.

To upgrade, first:

ets:insert(logplex_realtime,
           [{drain_dropped, 0}, {drain_delivered, 0}]).

Then load the logplex_realtime module, then the tcpsyslog drain module.
Alter drains to log messages delivered and dropped.