Implement .map(*) and map(*,...)

Mostly for consistency's sake and the fact that proto's are much cheaper now
Implement IO::Socket::Async.bytes_supply
Add IO/Socket/Async.pm to JVM build. Bump setting build heap to 1000m for Java 8.
Make .subst("a",:g) work
Bump NQP version to get async io ops on JVM.
Revert "Make .subst("a",:g) work"
Supply.migrate's supply should only take supplies
Also do the Supply.migrate tests
Merge pull request #266 from donaldh/jvm_async_ops

Implement IO::Socket::Async.bytes_supply and bump NQP_REVISION to get async ops on JVM.
Make sure we do the Supply.start tests
tools: only set $impl{config} when it is trueish

Otherwise we pass a ref of an empty hash around, wich will be treated truesh later.
more guidance to build rakudo

It shows examples what option can be passes, and it also mentiones
other backends than Parrot when someone tried to build for several
backends but did not supply the right flags.
Make Supply methods picker about what to accept

Specifically as to being called as a class or instance method.
Make sure we do Supply.schedule_on tests
Implement Supply.last
Guard Supply.last a bit against garbage input
Make sure we run the Supply.last tests
@a.splice(0,1) is @a.shift, you dummy!  :-)
Implement Supply.grab(&when_done)
Make sure we do the Supply.grab tests