New doc & doc fixes. Remove s_char on the way.

(C_MOD): Turn into enumeration constant.

src/lib/player/empdis.c

@@ -63,6 +63,8 @@ static int player_commands_index = 0;
 
 /*
  * Get a command from the current player into COMBUFP[1024], in UTF-8.
+ * This may block for input, yielding the processor.  Flush buffered
+ * output when blocking, to make sure player sees the prompt.
  * Return command's byte length on success, -1 on error.
  */
 int