Merging with leon master.Need to compare performance of lazy verificatoin

.gitignore

.larabot.conf

build.sbt

library/annotation/package.scala

library/collection/package.scala

library/lang/Either.scala

library/lang/StrOps.scala

library/lang/package.scala

library/lang/string/String.scala

library/lang/string/package.scala

src/main/isabelle/Leon_Library.thy

src/main/java/leon/codegen/runtime/StrOps.java

src/main/scala/leon/Main.scala

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

src/main/scala/leon/codegen/CompilationUnit.scala

src/main/scala/leon/datagen/GrammarDataGen.scala

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

src/main/scala/leon/evaluators/CodeGenEvaluator.scala

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

src/main/scala/leon/evaluators/StringTracingEvaluator.scala