Use const char pointers when possible in botlib's libvar code

code/botlib/botlib.h

@@ -409,9 +409,9 @@ typedef struct botlib_export_s
 	//shutdown the bot library, returns BLERR_
 	int (*BotLibShutdown)(void);
 	//sets a library variable returns BLERR_
-	int (*BotLibVarSet)(char *var_name, char *value);
+	int (*BotLibVarSet)(const char *var_name, const char *value);
 	//gets a library variable returns BLERR_
-	int (*BotLibVarGet)(char *var_name, char *value, int size);
+	int (*BotLibVarGet)(const char *var_name, char *value, int size);
 
 	//sets a C-like define returns BLERR_
 	int (*PC_AddGlobalDefine)(char *string);