Update to JuMP v1.15 nonlinear syntax

[odow]

Only substantive change is from a registered function for the head loss to something that is now traceable.

x-ref lanl-ansi/PowerModels.jl#858

Closes #61
Closes #156

[codecov]

Codecov Report

Merging #155 (873e174) into master (df331a2) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #155      +/-   ##
==========================================
- Coverage   92.04%   91.99%   -0.05%     
==========================================
  Files          39       39              
  Lines        4198     4174      -24     
==========================================
- Hits         3864     3840      -24     
  Misses        334      334              

Files Changed	Coverage Δ
src/prob/wf.jl	100.00% <ø> (ø)
src/core/function.jl	100.00% <100.00%> (ø)
src/form/crd.jl	100.00% <100.00%> (ø)
src/form/nc.jl	99.26% <100.00%> (ø)
src/form/ncd.jl	95.52% <100.00%> (ø)

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[odow]

I don't understand the 1.6 failure. That just seems wrong. Statistics is a stdlib...

[odow]

@ccoffrin this is ready to go on my end

[tasseff]

Looks great! Thanks, @odow! Super excited by the new nonlinear interface.

[ccoffrin]

LGTM. Before tagging the next release we should also make sure to fix #156 (which is many be covered in this PR as well)

[odow]

I just realized one potential issue: do you have projects that integrate PowerModels and WaterModels? If so, if one use the @NL syntax and one uses the new syntax, they're going to error.

[ccoffrin]

We do have some packages that combine the infrastructure models packages. These are the ones I can think of off the top of my head,
https://github.com/lanl-ansi/PowerModelsITD.jl
https://github.com/lanl-ansi/GasPowerModels.jl
https://github.com/lanl-ansi/PowerWaterModels.jl

As long long as the version of each package that updates to the new NL interface is a breaking release then the package version requirements should prevent incompatible versions. However, I do think we should put a concerted effort into updating the whole ecosystem to the new NL interface, so the packages can still interoperate as they progress.