leon.collection set operations

library/collection/package.scala

src/main/scala/leon/codegen/CodeGeneration.scala

src/main/scala/leon/datagen/VanuatooDataGen.scala

src/main/scala/leon/evaluators/RecursiveEvaluator.scala

src/main/scala/leon/frontends/scalac/CodeExtraction.scala

src/main/scala/leon/utils/Library.scala

src/test/scala/leon/test/codegen/CodeGenTests.scala