Add support for MOI.NumberOfThreads

[hannes-uppman]

Closes #220

[odow]

I avoided adding this previously because of #186

Cbc.jl/src/MOI_wrapper/MOI_wrapper.jl

Lines 136 to 142 in f495d97

	if param.name == "threads" && Sys.iswindows()
	@warn(
	"Ignoring threads parameter due to known bugs in CBC. Read " *
	"https://github.com/jump-dev/Cbc.jl/issues/186 for more details.",
	)
	return
	end

But I guess it doesn't hurt.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.37% 🎉

Comparison is base (f495d97) 87.67% compared to head (17f952e) 88.05%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #221      +/-   ##
==========================================
+ Coverage   87.67%   88.05%   +0.37%     
==========================================
  Files           2        2              
  Lines         349      360      +11     
==========================================
+ Hits          306      317      +11     
  Misses         43       43              

Files Changed	Coverage Δ
src/MOI_wrapper/MOI_wrapper.jl	88.25% <100.00%> (+0.38%)	⬆️

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[hannes-uppman]

I see.
Would it be better to have MOI.supports(::Optimizer, ::MOI.NumberOfThreads) return false on Windows?
Not having support on e.g. Linux because of a problem on Windows seems bad.

[odow]

I think this is fine to say "yes" and then throw a warning. I'm taking a look at the segfault issue. It used to be very sporadic. But it seems regular now.

[hannes-uppman]

Ok! Thanks!