[Teton] Handle Tab and Backspace.

lib/mammoth/input/keyboard.cpp

@@ -102,6 +102,8 @@ void KeyboardListenerBase::HandleKeycode(Keycode code, Action action) {
       c = ' ';
     } else if (code == kTab) {
       c = '\t';
+    } else if (code == kBackspace) {
+      c = '\b';
     } else if (code == kLShift) {
       lshift_ = true;
     } else if (code == kRShift) {

sys/teton/framebuffer/console.cpp

@@ -7,6 +7,16 @@ void Console::WriteChar(char c) {
     CursorReturn();
     return;
   }
+  if (c == '\t') {
+    WriteString("    ");
+    return;
+  }
+  if (c == '\b') {
+    cursor_pos_--;
+    WriteChar(' ');
+    cursor_pos_--;
+    return;
+  }
 
   uint64_t row = cursor_pos_ / cols();
   if (row >= rows()) {