Unify include guard styles and header comments.

include/mruby/error.h

 /*
-** error.h - Exception class
+** mruby/error.h - Exception class
 **
 ** See Copyright Notice in mruby.h
 */

include/mruby/gc.h

 /*
-** gc.h - garbage collector for mruby
+** mruby/gc.h - garbage collector for mruby
 **
 ** See Copyright Notice in mruby.h
 */

include/mruby/khash.h

@@ -4,8 +4,8 @@
 ** See Copyright Notice in mruby.h
 */
 
-#ifndef KHASH_H
-#define KHASH_H
+#ifndef MRUBY_KHASH_H
+#define MRUBY_KHASH_H
 
 #if defined(__cplusplus)
 extern "C" {
@@ -267,4 +267,4 @@ typedef const char *kh_cstr_t;
 }  /* extern "C" { */
 #endif
 
-#endif  /* KHASH_H */
+#endif  /* MRUBY_KHASH_H */

include/mruby/opcode.h

 /*
-** opcode.h - RiteVM operation codes
+** mruby/opcode.h - RiteVM operation codes
 **
 ** See Copyright Notice in mruby.h
 */
 
-#ifndef OPCODE_H
-#define OPCODE_H
+#ifndef MRUBY_OPCODE_H
+#define MRUBY_OPCODE_H
 
 #define MAXARG_Bx        (0xffff)
 #define MAXARG_sBx       (MAXARG_Bx>>1)         /* `sBx' is signed */
@@ -157,4 +157,4 @@ enum {
 #define OP_R_BREAK  1
 #define OP_R_RETURN 2
 
-#endif  /* OPCODE_H */
+#endif  /* MRUBY_OPCODE_H */

include/mruby/version.h

+/*
+** mruby/version.h - mruby version definition
+**
+** See Copyright Notice in mruby.h
+*/
+
 #ifndef MRUBY_VERSION_H
 #define MRUBY_VERSION_H