Add basic PTY support.

For now, there are four hard-coded PTYs: /dev/pt{m,s}[0123]
Use this in the Terminal to open a pty pair and spawn a shell.

Kernel/SlavePTY.cpp

@@ -0,0 +1,30 @@
+#include "SlavePTY.h"
+#include "MasterPTY.h"
+
+SlavePTY::SlavePTY(unsigned index)
+    : TTY(11, index)
+    , m_index(index)
+{
+}
+
+SlavePTY::~SlavePTY()
+{
+}
+
+String SlavePTY::tty_name() const
+{
+    char buffer[32];
+    ksprintf(buffer, "/dev/pts%u", m_index);
+    return buffer;
+}
+
+void SlavePTY::on_master_write(const byte* buffer, size_t size)
+{
+    for (size_t i = 0; i < size; ++i)
+        emit(buffer[i]);
+}
+
+void SlavePTY::on_tty_write(const byte* data, size_t size)
+{
+    m_master->on_slave_write(data, size);
+}