Build fixes; license; groupId = org.scala-lang.modules

The license is a standard 3-clause BSD license.

We're publishing modules under org.scala-lang.modules.
This signals they are "just another Scala library":
  - cross-versioned (cross-versioning under org.scala-lang confuses sbt)
  - backward binary compatible (but not forward like the core)

Compile under Optimize/Deprecation/Features/Lint.

Fix deprecation errors:
Don't call log in ValidatingMarkupHandler, CachedFileStorage anymore,
as that generates deprecation messages, and apparently we should use
a debugger to debug.