As part of the ANZ "go" course the first lab is to produce a piece of software
that will produce the Fibonacci series for fib(7).
It was also an exercise in the tour.golang.org.
Generating the series was implemented as "closure" which was a requirement in
the tour-golang . There are other ways to solve this problem,
but I kept it as an example of closure for later reference.
The function maintains state and hence has to be called sequentially.