WTF ?! basic computations are faster in py3 than nim1.6 ?!

[cblake]

Note - your playground benchmark looks like it does an `assert` line for the 
main work which may be **_optimized away completely_** by the compiler. You may 
want to ensure you use the value somehow (like adding it up and printing it out 
at the end) - that way it would be illegal to not run the calculation.