Change char->free to auto_char char for autocleanup

Replace `gchar` and `g_free` to `auto_gchar`
Correct certain  `char` functions/variables to `gchar`

Related to #1819.

Edited by @jubalh.

src/command/cmd_defs.c

@@ -3052,13 +3052,12 @@ command_mangen(void)
     while (curr) {
         Command* pcmd = curr->data;
 
-        gchar* filename = g_strdup_printf("docs/profanity-%s.1", &pcmd->cmd[1]);
+        auto_gchar gchar* filename = g_strdup_printf("docs/profanity-%s.1", &pcmd->cmd[1]);
         if (!filename) {
             log_error("command_mangen(): could not allocate memory");
             return;
         }
         FILE* manpage = fopen(filename, "w");
-        free(filename);
 
         fprintf(manpage, "%s\n", header);
         fputs(".SH NAME\n", manpage);