Standardise header include guards

Tokens that begin with two underscores __* or an underscore and an uppercase letter _X* are reserved,
so we should avoid those for our own include guards.  The standard I'm settling on for foo.h is FOO_H_.

include/chelp.h

@@ -3,9 +3,8 @@
  * 
  *
  */
-
-#ifndef __chelp_h
-#define __chelp_h
+#ifndef CHELP_H_
+#define CHELP_H_
 
 extern void chelp (char *, char *, char *, char *);