more precise control and verbose logging for proguard task

[ezh]

we may add our proguard.cfg settings to proguardOptions with

proguardOption in Android <+= (baseDirectory) map { (b) => scala.io.Source.fromFile(b / "proguard.cfg").mkString }

or we may completely override proguardOptions with

proguardOption in Android <<= (baseDirectory) map { (b) => scala.io.Source.fromFile(b / "proguard.cfg").mkString :: Nil }

also add more verbose logging

[debug] executing proguard: arg1: -injars
[debug] arg2: "/hom....
[debug] arg3: -outjars
[debug] arg4: "/home/devbox/android/android-DigiLib/test/testPublicProperties/bin/target/classes.min.jar"
[debug] arg5: -libraryjars
[debug] arg6: "/home/devbox/android/android-sdk-linux/platforms/android-10/android.jar"
[debug] arg7: -dontoptimize

it is handy to fix errors like

android:proguard: proguard.ParseException: NNNNN in argument number 20