Introduce LetPattern, LetTuple specializes it for TuplePatterns

project/build.properties

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

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

src/main/scala/leon/purescala/Constructors.scala

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

src/main/scala/leon/purescala/PrettyPrinter.scala

src/main/scala/leon/purescala/ScopeSimplifier.scala

src/main/scala/leon/purescala/TransformerWithPC.scala

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

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

src/main/scala/leon/purescala/TypeTreeOps.scala

...main/scala/leon/solvers/templates/TemplateGenerator.scala

src/main/scala/leon/solvers/z3/AbstractZ3Solver.scala

src/main/scala/leon/synthesis/utils/ExpressionGrammar.scala