Break inclusion cycle: prototypes.h and commands.h included each

other.  Ensure headers in include/ can be included in any order
(except for econfig-spec.h, which is special).  New header types.h to
help avoid inclusion cycles.  Sort include directives.  Remove some
superflous includes.

src/lib/commands/capi.c

@@ -34,13 +34,6 @@
 
 #include <config.h>
 
-#include "misc.h"
-#include "player.h"
-#include "sect.h"
-#include "nat.h"
-#include "xy.h"
-#include "nsc.h"
-#include "file.h"
 #include "commands.h"
 
 int