added IPC syscalls

kernel/syscall/skeleton.h

@@ -26,6 +26,11 @@ void kill(Vault &vault, size_t pid);
 void* map(Vault *vault, size_t size);
 int unmap(Vault &vault, void* start, size_t size);
 void invlpg(uintptr_t virt_addr);
+bool send(Vault &vault, int pid, const void* sbuffer, size_t ssize, void* rbuffer, size_t rsize);
+int receive(Vault &vault, void* buffer, size_t size);
+bool reply(Vault &vaul, const void* buffer, size_t size);
+//int fork(Vault &vault, InterruptContext *user);
+
 
 }  // namespace Skeleton
 }  // namespace Syscall