Split maxscale.h to public and private parts

This header defines some general functions and maxscale main() return
values. Most of it is still public, but there were some functions
which were moved to a core header.

server/core/misc.c

@@ -12,31 +12,22 @@
  */
 
 #include <maxscale/maxscale.h>
+
 #include <time.h>
+#include "maxscale/maxscale.h"
 
 static time_t started;
 
-/**
- * Reset the start time from which the uptime is calculated.
- */
 void maxscale_reset_starttime(void)
 {
     started = time(0);
 }
 
-/**
- * Return the time when MaxScale was started.
- */
 time_t maxscale_started(void)
 {
     return started;
 }
 
-/**
- * Return the time MaxScale has been running.
- *
- * @return The uptime in seconds.
- */
 int maxscale_uptime()
 {
     return time(0) - started;