sbt 0.13 upgrade: avoid deprecated sbt APIs
sbt 0.13: eliminate Build.scala using 0.13 features
sbt 0.13: cleanup using new macros

if not specifying the `test` scope on these breaks anything, I don't
know what it is. the new inputKey macro doesn't take scope arguments
like the old InputKey.apply did
sbt 0.13: minor cleanup using new macros
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sbt 0.13: little syntax improvements