Commit 87d33b6c9e added code which uses bool.
Therefore stdbool.h must be included for compilations with a C compiler.
Signed-off-by: Stefan Weil <sw@weilnetz.de>
The C API is missing the ability to monitor the progress of the
recognition. This patch adds C wrappers to the progress monitor
that allow monitoring the progress and canceling the recognition
process early.