Consolidation with CDI-PIO (develop)

Generally, this is !11 (merged) rebased onto the develop branch.

This is the first develop-based version accepted by the Buildbot of ICON: https://buildbot.dkrz.de/grid?branch=m300488/cdi-pio-2-integration

src/pio_client.c

@@ -4,6 +4,7 @@
 
 #include <ctype.h>
 #include <errno.h>
+#include <stdbool.h>
 
 #include <yaxt.h>