Support for both Windows and Linux newlines and don't split lines

I noticed that when a line got split when writing logstash-forwarder either sent both halves of the line as separate events or detected it as a file truncation. Besides, the +1 on the offset assumed only linux type newlines (\n) and could have funky behavior with windows style newlines (\r\n).

I changed the code a bit to allow the files being monitored to have split lines momentarily, I hope it can help someone.