Deprecate UnconstrainedProblems / add getproblem API

[anriseth]

Ref #9 (comment)

[pkofod]

Yes, that's exactly what I mean. If you tag this package now, Optim will break, so you have to put an upper bound on Optim and that's annoying. Or am I misunderstanding?

[anriseth]

It won't break, as I added backwards-compatibility in the PR. See, for example, https://github.com/JuliaNLSolvers/OptimTestProblems.jl/blob/master/src/OptimTestProblems.jl#L8. The annoying thing is that I don't know how to tell the user to stop using the legacy stuff.

[anriseth]

Just to be clear, the two things that I want to deprecate are
https://github.com/JuliaNLSolvers/OptimTestProblems.jl/blob/master/src/OptimTestProblems.jl#L8
https://github.com/JuliaNLSolvers/OptimTestProblems.jl/blob/master/src/optim_tests/multivariate/unconstrained.jl#L7

[pkofod]

Ah, perfect then! Anyway, we're the only users here. The lesson is to use something like getproblem() instead of dictionaries for stuff like this. If something could be deprecated at some point, it's always better to use a function.