Adapt everything in BT5 to new capnhook API

This includes:
- Renaming of functions (iohook_invoke_next)
- Slight interface changes (com_proxy_wrap, iohook_push_handler)
- De-duplicate stuff from utils (iobuf, hr)

src/main/jbhook/acio.c

@@ -53,7 +53,7 @@ ac_io_port_dispatch_irp(struct irp *irp)
     log_assert(irp != NULL);
 
     if (!ac_io_emu_match_irp(&ac_io_emu, irp)) {
-        return irp_invoke_next(irp);
+        return iohook_invoke_next(irp);
     }
 
     for (;;) {

src/main/jbhook/dllmain.c

@@ -32,11 +32,6 @@
 
 static struct options options;
 
-static const irp_handler_t jbhook_handlers[] = {
-    p4ioemu_dispatch_irp,
-    ac_io_port_dispatch_irp,
-};
-
 static bool my_dll_entry_init(char *sidcode, struct property_node *param)
 {
     bool eam_io_ok;
@@ -132,7 +127,9 @@ BOOL WINAPI DllMain(HMODULE mod, DWORD reason, void *ctx)
     options_init_from_cmdline(&options);
 
     app_hook_init(my_dll_entry_init, my_dll_entry_main);
-    iohook_init(jbhook_handlers, lengthof(jbhook_handlers));
+
+    iohook_push_handler(p4ioemu_dispatch_irp);
+    iohook_push_handler(ac_io_port_dispatch_irp);
 
     if (!options.disable_adapteremu) {
         adapter_hook_init();