Use FastBroadcast for multithreaded broadcasting?

For some time we've lamented that while FFTW is multithreaded, broadcasting operations such as

https://github.com/FourierFlows/FourierFlows.jl/blob/e059ba96260f483b493659fcefb343a08f0db9ae/src/timesteppers.jl#L109

are not. 

`FastBroadcast.jl` provides an answer:

https://github.com/YingboMa/FastBroadcast.jl

It seems that even without multithreading, it can speed things up.