* New process-control RPC feature in clixon-lib.yang to manage processes

* This is an alternative to manage a clixon daemon via sudtemd, containerd or other
  * One important special case is starting the clixon-restconf daemon internally
  * This is how it works:
    * Register a process via `clixon_process_register(h, name, namespace, argv, argc)`
    * Use process-control RPC defined in clixon-lib.yang to start/stop/restart or query status on that process
  * Example code in the main example

lib/clixon/clixon.h.in

@@ -77,6 +77,7 @@ extern "C" {
 #include <clixon/clixon_yang_type.h>
 #include <clixon/clixon_event.h>
 #include <clixon/clixon_string.h>
+#include <clixon/clixon_proc.h>
 #include <clixon/clixon_file.h>
 #include <clixon/clixon_xml.h>
 #include <clixon/clixon_xml_sort.h>