Hello,
i have created a mini tool for automatically increment a build number and also at the same time modify the AndroidManifest file.
In my header file, i define 3 var :
Build, Major, Minor
The tool increment the Build var. Major and minor are user defined.
android:versionCode = Build
android:versionName = Major.Minor.Build
Here the tool if many are interested by it: https://github.com/aiekick/BuildIncrement