Write a simple DNS example using pseudo-spectral solver

[jiweiqi]

Example of non-reacting flow at https://github.com/loiseaujc/NS2D.jl

[RSuryaNarayan]

Are we attempting a simple reacting DNS? Then I think a premixed laminar methane-bunsen flame would be a really good idea. We got GRImech30 for the chemistry and we would just need to whip up the CFD aspects of it