Lots of hacking:

- Turn Keyboard into a CharacterDevice (85,1) at /dev/keyboard.
- Implement MM::unmapRegionsForTask() and MM::unmapRegion()
- Save SS correctly on interrupt.
- Add a simple Spawn syscall for launching another process.
- Move a bunch of IO syscall debug output behind DEBUG_IO.
- Have ASSERT do a "cli" immediately when failing.
  This makes the output look proper every time.
- Implement a bunch of syscalls in LibC.
- Add a simple shell ("sh"). All it can do now is read a line
  of text from /dev/keyboard and then try launching the specified
  executable by calling spawn().

There are definitely bugs in here, but we're moving on forward.

Kernel/Keyboard.h

@@ -1,16 +1,25 @@
 #pragma once
 
 #include <AK/Types.h>
+#include <AK/DoublyLinkedList.h>
+#include <AK/CircularQueue.h>
+#include <VirtualFileSystem/CharacterDevice.h>
 #include "IRQHandler.h"
 
-class Keyboard final : public IRQHandler {
+class Keyboard final : public IRQHandler, public CharacterDevice {
 public:
     virtual ~Keyboard() override;
     Keyboard();
 
 private:
+    // ^IRQHandler
     virtual void handleIRQ() override;
 
+    // ^CharacterDevice
+    virtual ssize_t read(byte* buffer, size_t) override;
+    virtual ssize_t write(const byte* buffer, size_t) override;
+
+    CircularQueue<byte, 16> m_queue;
     byte m_modifiers { 0 };
 };