Basic ^C interrupt implementation.

For testing, I made cat put itself into a new process group.
This should eventually be done by sh between fork() and exec().

Kernel/Keyboard.h

@@ -6,15 +6,25 @@
 #include <VirtualFileSystem/CharacterDevice.h>
 #include "IRQHandler.h"
 
-class KeyboardClient {
-public:
-    virtual ~KeyboardClient();
-    virtual void onKeyPress(byte) = 0;
-};
+class KeyboardClient;
 
 class Keyboard final : public IRQHandler, public CharacterDevice {
     AK_MAKE_ETERNAL
 public:
+    enum Modifier {
+        Mod_Alt = 0x01,
+        Mod_Ctrl = 0x02,
+        Mod_Shift = 0x04,
+    };
+
+    struct Key {
+        byte character { 0 };
+        byte modifiers { 0 };
+        bool alt() { return modifiers & Mod_Alt; }
+        bool ctrl() { return modifiers & Mod_Ctrl; }
+        bool shift() { return modifiers & Mod_Shift; }
+    };
+
     static Keyboard& the() PURE;
 
     virtual ~Keyboard() override;
@@ -34,7 +44,12 @@ private:
     void emit(byte);
 
     KeyboardClient* m_client { nullptr };
-    CircularQueue<byte, 16> m_queue;
+    CircularQueue<Key, 16> m_queue;
     byte m_modifiers { 0 };
 };
 
+class KeyboardClient {
+public:
+    virtual ~KeyboardClient();
+    virtual void onKeyPress(Keyboard::Key) = 0;
+};