Set minSdk and compileSdkVersion to 21 and 31...

Bumped C++ version to 20.
Updated .gitignore

module/build.gradle.kts

@@ -12,8 +12,9 @@ val abiList: List<String> by rootProject.extra
 
 android {
     namespace = "com.example.library"
-    compileSdk = 34
+    compileSdkVersion = "android-31"
     defaultConfig {
+        minSdk = 21
         ndk {
             abiFilters.addAll(abiList)
         }