Add step mode to z3ed cli emulator

src/cli/command_handler.h

@@ -282,13 +282,37 @@ class Emulator : public CommandHandler {
     std::string filename = arg_vec[0];
     RETURN_IF_ERROR(rom_.LoadFromFile(filename))
 
+    bool step = false;
+    if (arg_vec[1].empty()) {
+      snes.SetCpuMode(0);
+    } else {
+      snes.SetCpuMode(1);
+      step = true;
+    }
+
     snes.SetupMemory(rom_);
     snes.Init(rom_);
 
-    int i = 0;
-    while (i < 80000) {
-      snes.Run();
-      i++;
+    if (!step) {
+      int i = 0;
+      while (i < 80000) {
+        snes.Run();
+        i++;
+      }
+    } else {
+      // This loop should take in input from the keyboard, such as pressing
+      // space to step through the loop and pressing x to end the execution.
+      bool stepping = true;
+      std::cout << "Press space to step, x to exit" << std::endl;
+      while (stepping) {
+        char input;
+        std::cin.get(input);
+        if (input == 'x') {
+          break;
+        } else {
+          snes.StepRun();
+        }
+      }
     }
 
     return absl::OkStatus();