[FileFormats.MOF] Use JSON3 to write files

[joaquimg]

A test

using JuMP

model = Model()
@variable(model, x[1:1000] >= 0)
@constraint(model, y[1:1000], sum(i*x[i] for i in 1:1000) == 1)

for i in 1:5
    GC.gc()
    @time write_to_file(model, "test.mof.json")
end

Results:

before PR:

  3.312154 seconds (5.14 M allocations: 772.433 MiB, 6.80% gc time)
  3.546777 seconds (5.14 M allocations: 772.416 MiB, 6.70% gc time)
  3.368654 seconds (5.14 M allocations: 772.483 MiB, 6.37% gc time)
  3.924556 seconds (5.14 M allocations: 772.422 MiB, 6.55% gc time)
  3.771463 seconds (5.14 M allocations: 772.390 MiB, 6.51% gc time)

after PR:

  0.965306 seconds (9.63 M allocations: 577.394 MiB, 7.00% gc time)
  1.171944 seconds (9.63 M allocations: 577.394 MiB, 6.04% gc time)
  1.028857 seconds (9.63 M allocations: 577.394 MiB, 5.34% gc time)
  1.126085 seconds (9.63 M allocations: 577.394 MiB, 5.80% gc time)
  1.120570 seconds (9.63 M allocations: 577.394 MiB, 5.72% gc time)

[odow]

I'm not against this, but I'm not strongly in favor. Do you have a benchmark of the Sienna instance?

[odow]

If we do this, we should use JSON3 to replace all instances of JSON. Let's not have two packages floating around just for the sake of it.

[odow]

Okay, I did some tests locally with JSON3, and I'm happy now.