add encrypting for save files

add libhydrogen for encrypting and decrypting

#9

libs/libhydrogen/impl/random/esp32.h

@@ -0,0 +1,32 @@
+// Important: RF *must* be activated on ESP board
+// https://techtutorialsx.com/2017/12/22/esp32-arduino-random-number-generation/
+#ifdef ESP32
+#    include <esp_system.h>
+#endif
+
+#ifdef ARDUINO
+#    include <Arduino.h>
+#endif
+
+static int
+hydro_random_init(void)
+{
+    const char       ctx[hydro_hash_CONTEXTBYTES] = { 'h', 'y', 'd', 'r', 'o', 'P', 'R', 'G' };
+    hydro_hash_state st;
+    uint16_t         ebits = 0;
+
+    hydro_hash_init(&st, ctx, NULL);
+
+    while (ebits < 256) {
+        uint32_t r = esp_random();
+
+        delay(10);
+        hydro_hash_update(&st, (const uint32_t *) &r, sizeof r);
+        ebits += 32;
+    }
+
+    hydro_hash_final(&st, hydro_random_context.state, sizeof hydro_random_context.state);
+    hydro_random_context.counter = ~LOAD64_LE(hydro_random_context.state);
+
+    return 0;
+}