Basically, stream_socket_connect can't get any errors with that API.
for now, we rely error_get_last()'s message. fluent-logger will close the socket and
reconnect to the host if it contains `errno=32` (EPIPE).

[Changes]
 * add exponential backoff strategy for reconnecting issue and it becomes defualt back off strategy.
   also change default attempt count.
 * change method name: FluentLogger::clearInstances as fix typo.
 * fix many many typos. i can't believe why i missed those things.