Rework positions, introduce RangePositions

src/main/scala/leon/plugin/CodeExtraction.scala

src/main/scala/leon/purescala/Common.scala

src/main/scala/leon/purescala/Definitions.scala

src/main/scala/leon/purescala/Extractors.scala

src/main/scala/leon/purescala/FunctionClosure.scala

src/main/scala/leon/purescala/TreeOps.scala

src/main/scala/leon/purescala/Trees.scala

src/main/scala/leon/synthesis/FileInterface.scala

src/main/scala/leon/termination/TerminationPhase.scala

src/main/scala/leon/utils/Positions.scala

src/main/scala/leon/utils/UnitElimination.scala

src/main/scala/leon/verification/AnalysisPhase.scala

src/main/scala/leon/verification/DefaultTactic.scala

src/main/scala/leon/verification/InductionTactic.scala

src/main/scala/leon/verification/VerificationCondition.scala

src/main/scala/leon/verification/VerificationReport.scala

src/main/scala/leon/xlang/ArrayTransformation.scala

src/main/scala/leon/xlang/EpsilonElimination.scala

src/main/scala/leon/xlang/ImperativeCodeElimination.scala

src/main/scala/leon/xlang/Trees.scala