fix #75 -- error out if no valid platform targets
refactor proguard and projectlayout classes out of keys
0.13 changes
0.13 changes for 0.9.2
0.13 changes for test hello-world-oscarvarto
0.13.5 changes
fix #65 add AutoPlugin support, auto-enable with AutoBuild
Add aliases for AutoPlugin autoImport

aliases added for ProguardCache, ProguardInputs, apklib, aar,
AutoLibraryProject and LibraryProject