feat(furdb): add break command

furdb/include/command.hpp

@@ -36,4 +36,9 @@ public:
     void execute(context& ctx, const command_info& info) override;
 };
 
+class break_command final : public command {
+public:
+    void execute(context& ctx, const command_info& info) override;
+};
+
 #endif // COMMAND_HPP

furdb/include/context.hpp

@@ -13,6 +13,7 @@ struct context {
     furvm::function_h mainFunction;
 
     bool running = true;
+    bool halt    = false;
 
     void run();
 };