With these flags API consumers can optimize the depiction of libliftoff's debug
log.
For now the two flags for a section start and end are introduced. It is
guaranteed that one section always ends before the next one begins.
Is no callback function setup section starts and ends in the default stderr
output will be marked with an empty line.
BREAKING CHANGE: The signature of the log callback changes.
Instead of exposing to consumers write streaming log data into a per-device
buffer that gets created on request and destroyed after the buffer has been
written to the log.
Passing a NULL string to the internal continuous log function triggers a write
of the buffer to the log.
BREAKING CHANGE: continuous log function is moved from log header to private
header.
