Add build scripts and update .gitignore

This commit introduces build scripts for both Windows (`build.bat`) and Linux/macOS (`build.sh`) to simplify the build process.

It also updates the `.gitignore` file to a more comprehensive version that includes common patterns for C++ projects and various IDEs.

src/Library.cpp

@@ -0,0 +1,5 @@
+#include "Library.h"
+
+int add(int a, int b) {
+    return a + b;
+}

src/Library.h

@@ -0,0 +1,15 @@
+#pragma once
+
+// Define MY_LIB_EXPORT for exporting symbols from the DLL
+#if defined(_WIN32)
+    #if defined(MY_LIB_EXPORT)
+        #define MY_LIB_API __declspec(dllexport)
+    #else
+        #define MY_LIB_API __declspec(dllimport)
+    #endif
+#else
+    #define MY_LIB_API
+#endif
+
+// A simple function to be exported
+MY_LIB_API int add(int a, int b);