experimental config option TTY_PERM_INVENT

Add a rudimentary experimental always-up inventory display
capability to tty when the perm_invent option is in effect.
It requires an additional 28 rows available on the terminal
underneath the bottom status line.

It hasn't been optimized for performance as of yet.

src/decl.c

@@ -435,6 +435,9 @@ const struct instance_globals g_init = {
     NULL, /* invbuf */
     0, /* inbufsize */
     WIN_ERR, /* cached_pickinv_win */
+#ifdef TTY_PERM_INVENT
+    WIN_ERR, /* tty_invent_win */
+#endif
     0, /* this_type */
     NULL, /* this_title */
     UNDEFINED_VALUES, /* only (coord) */