Decrease cyclomatic complexity

[ainar-g]

Right now we set gocyclo to allow the maximum cyclomatic complexly of of 20. McCabe originally recommended to limit the value to no more than 10, but NIST later observed that values up to 15 may be allowed in some cases. I think we should at least strive to decrease it to 15 and see if continuing will do more good than harm.

I also don't think that decreasing it all in one go is a good choice, so I'll make this ticket a recurrent one and gradually decrease the complexity as we go.

[ainar-g]

We were able to decrease the maximum complexity to 17 in this cycle. We'll try to reach 15 in the next cycle.