Playing with Coroutines

Using goroutines to implement coroutines in Go. I am following the
example given here
:http://www.golangpatterns.info/concurrency/coroutines though I had to
amend it since Go does not support nested func declarations. Notice
that on the fibonacci sequence generator we relatively quickly hit the
overflow on the int type. Hence, one should probably use unsigned longs
for this kind of thing.