[Assignment-7] Flake + App base

- Add Assignment-7 to flake.nix
- Implement basic framework of app
- Implement proxy subcommand (mostly)
- Implement basics of intermediary subcommand

7-SGX_Hands-on/src/app/util.h

@@ -0,0 +1,13 @@
+#ifndef _APP_UTIL_H_
+#define _APP_UTIL_H_
+
+
+char* BIN_NAME;
+
+/*
+ * @brief prints the command syntax and exits with EXIT_FAILURE
+ */
+void syntax_exit(void);
+
+
+#endif