Refactor: Restructure project package hierarchy and add initial implementation for assembler instructions, shell commands, and exception handling.

src/jvmMain/kotlin/mtmc/os/shell/builtins/ExitCommand.kt

@@ -0,0 +1,15 @@
+package mtmc.os.shell.builtins
+
+import mtmc.emulator.MonTanaMiniComputer
+import mtmc.os.shell.ShellCommand
+import mtmc.tokenizer.MTMCTokenizer
+
+class ExitCommand : ShellCommand() {
+  public override fun exec(tokens: MTMCTokenizer, computer: MonTanaMiniComputer) {
+    computer.console.println("Goodbye!")
+    System.exit(1)
+  }
+
+  override val help: String
+    get() = "exit - exits the system"
+}