support of async expression inside well-known higth-order functions

• added support for select.timeout construct
• added support for lifting-up await in hight-order functions.
  ie in simplicified explanation:

 for(x <- 1 to n) { s += read(x) }

is translated to

 1.to(n).foreachAsync { async(s += await(aread(x))) }

details can be found in techreport: https://arxiv.org/abs/1611.00602

• added support for select.fold construct
• scala 2.12