set VERSION = 0.11.0.preview1
BufferedOutput::FlushThread should not block for long time
refactored comments in in_tail

we don't need to use 'watchr' because Coolio already uses
'inotify' internally in case of Linux.
flush_interval accepts seconds less than 1.0
updated msgpack dependency to 0.5.7
BufferedOutput#write_abort calls Buffer#clear
Merge v11 branch
Update example configurations