Change special keys into extended commands

Changes most of the special keys used in the main input loop
into extended commands:

- movement keys are now bound to extended commands, eg.
  #movewest and so on.

- m-prefix is now #reqmenu extended command, still bound to
  the 'm' key.

- run, rush, and fight are now extended commands, still bound
  to the same keys as previously.

- nopickup and runnopickup keys are removed.
  Nopickup was using 'm' key, the same as the m-prefix, so
  allow #reqmenu to modify movement commands to disable pickup.

- multiple prefix commands are allowed. This lets user to
  use #reqmenu, followed by #run, followed by movement to simulate
  runnopickup behaviour. (If necessary, adding runnopickup back
  as an extended command would be easy)

include/func_tab.h

@@ -15,6 +15,8 @@
 #define NOFUZZERCMD  0x20 /* fuzzer cannot execute this command */
 #define INTERNALCMD  0x40 /* only for internal use, not for user */
 #define CMD_M_PREFIX 0x80 /* accepts menu prefix */
+#define PREFIXCMD    0x100 /* prefix command, requires another one after it */
+#define MOVEMENTCMD  0x200 /* used to move hero/cursor */
 
 struct ext_func_tab {
     uchar key;