Use FastPower.jl for faster power function

[visr]

This package was registered today: https://github.com/SciML/FastPower.jl
I remember from profiling a while ago that the power function was the main bottleneck for the kinematic wave. So I wonder how much difference this trade of precision for performance will be. This function by itself is about 2-2.5x faster.

[visr]

Wow I'm surprised, but this actually leads to significantly worse performance. It looks like with the lower power precision the kinematic wave doesn't convergence well. The epsilon of 1e-12 may just be too low, making it hit the max_iters instead.

Wflow.jl/src/horizontal_process.jl

Lines 27 to 29 in 8a4d2e9

	function kinematic_wave(Qin, Qold, q, alpha, beta, dt, dx)
	epsilon = 1.0e-12
	max_iters = 3000

If I set the epsilon higher, the performance difference goes down.