Size-based rotation

Size-based rotation

The user can now configure the desired size of each chunk, every time a
chunk is bigger than the specified size, a rotation is automatically
started. The size of a chunk is measured by polling from the monitoring
thread, so the accuracy depends on the monitoring sampling rate.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>