Stratified Couette flow verification

[ali-ramadhan]

This PR introduces a script for simulating Stratified Couette flow with the aim of reproducing the LES results of Vreugdenhil & Taylor (2018). See #310 for more details.

When the verification is completely successfully, I will ensure the script is maintained in the test/verification/ subdirectory so that the verification can be reproduced at any time. I will also convert it to a regression test. See #347.

Resolves #310
Resolves #415
Contributes to #346 and #347

[codecov]

Codecov Report

Merging #381 into master will increase coverage by 0.42%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #381      +/-   ##
==========================================
+ Coverage   71.65%   72.07%   +0.42%     
==========================================
  Files          26       26              
  Lines        1418     1418              
==========================================
+ Hits         1016     1022       +6     
+ Misses        402      396       -6

Impacted Files	Coverage Δ
src/diagnostics.jl	79.66% <0%> (+3.38%)	⬆️
src/utils.jl	83.51% <0%> (+4.39%)	⬆️

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[glwagner]

Is "verification" just a run script, or do we include analysis as well? Maybe need to have a folder for each verification case?

[ali-ramadhan]

Thanks for the comments!

Is "verification" just a run script, or do we include analysis as well? Maybe need to have a folder for each verification case?

Yeah a folder for each might make sense. I'm envisioning that each verification test case is described in the documentation with enough figures/plots to convince the reader that Oceananigans is doing the right thing. There should be a simulation script (like the one in this PR) that allows the reader to reproduce the simulation, and probably one or more plotting scripts allowing them to recreate the plots.