Using this `LoggingManager` all the log flows (reading and writing) were
refactored. Inteface of `LoggingManager` should be now generic enough to
replace log handling with almost any implementation - log rotation,
sending logs to remote destination, keeping logs in memory, etc.
There should be no functional changes.
As part of changes, `follow.Reader` was implemented which makes
appending file feel like a stream. `file.NewChunker` was refactored to
use `follow.Reader` and `stream.NewChunker` to do the actual work. So
basically now we have only a single instance of chunker - stream
chunker, as everything is represented as a stream.
Signed-off-by: Andrey Smirnov <smirnov.andrey@gmail.com>