Add collectIn combinator, change ScalametaTraverserHelperMacros to older version because of too long compile times
Fixed update. Use lub instead of glb
use buildFromTopSymbol instead of buildFromTopSymbolOptimize
Change return type of filter and update combinators
add stateful combinator (with laziness)
add andThenLeft combinator
simplyfy implementation of CollectIn
simplify implementation of stateful combinator
Simplify implementation of visit combinator
Change update macro so that it accepts to pass partial functions around.

Need to use a runtime asInstanceOf since c.untypecheck doesn't work with extractors in pattern matching (see https://issues.scala-lang.org/browse/SI-8825)