Fixes and new apps (#30)

- M5 Unit Modules library + M5 Unit Test app
- Minor fixes for TodoList, TwoEleven, Snake, Brainfuck and Breakout
- Fixed SerialConsole to use the uart controller as it was broken in one of the many updates
- Fixed keyboard input in TwoEleven, Breakout, Magic8Ball and Snake
- Bluetooth Media Keys app, supports pressing physical keys to trigger the corresponding buttonmatrix button
- Epub Reader app

Libraries/M5UnitModules/Include/UnitPaHub.h

@@ -0,0 +1,50 @@
+/*
+ * UnitPaHub.h - M5Stack PaHub v2 I2C multiplexer (TCA9548A, addr 0x70)
+ *
+ * 6-channel I2C mux. Selecting a channel routes the downstream bus to that
+ * port only. Selecting channel 255 (or calling deselect()) disables all ports.
+ *
+ * Usage:
+ *   UnitPaHub hub;
+ *   if (hub.begin(dev)) {
+ *       hub.select(0);           // enable channel 0
+ *       enc.begin(dev);          // devices on channel 0 now reachable
+ *       hub.deselect();          // disable all channels when done
+ *   }
+ *
+ * Note: for devices that stay selected for extended periods (e.g. polling),
+ * leave the channel selected - only call deselect() if you need to prevent
+ * address conflicts between units on different channels.
+ */
+#pragma once
+
+#include <UnitCommon.h>
+#include <cstdint>
+
+class UnitPaHub {
+public:
+    UnitPaHub() = default;
+    UnitPaHub(const UnitPaHub&) = delete;
+    UnitPaHub& operator=(const UnitPaHub&) = delete;
+
+    static constexpr uint8_t DEFAULT_ADDR    = 0x70;
+    static constexpr uint8_t NUM_CHANNELS    = 6;
+    static constexpr uint8_t NO_CHANNEL      = 0xFF;
+
+    // Pass a I2C controller device
+    bool begin(Device* dev, uint8_t addr = DEFAULT_ADDR);
+    bool isPresent() const { return dev_ != nullptr; }
+
+    // Select a single channel (0-5). Returns false on error.
+    bool select(uint8_t channel);
+
+    // Disable all channels.
+    bool deselect();
+
+    uint8_t currentChannel() const { return channel_; }
+
+private:
+    Device*  dev_     = nullptr;
+    uint8_t  addr_    = DEFAULT_ADDR;
+    uint8_t  channel_ = NO_CHANNEL;
+};