Currently hints are processed only once the process is finished and
exits with non-error exit code. In interactive mode, e.g. for monitor,
we want to process ouput lines for hints right away.
This adds a simple buffer, which keeps the last line and once EOL is
reached, it is processed for hints.
Since the original hints processing was file based, a new helper
function was added to allow processing hints in string.
Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>
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