Action bar add
http://developer.android.com/training/basics/actionbar/index.html
Beginning with Android 3.0 (API level 11), the action bar is included in all activities that use the Theme.Holo theme (or one of its descendants), which is the default theme when either the targetSdkVersion or minSdkVersion attribute is set to "11" or greater. So we change theme version to Theme.AppCompat.Light and make MainActivity extends ActionBarActivity

The lint.xml file
A configuration file that you can use to specify any lint checks that you want to exclude and to customize problem severity levels.
http://developer.android.com/tools/help/lint.html