Fix warning on non-finite nadir point

[odow]

Closes #60

From a quick survey of some papers, it seems that computing the nadir point is non-trivial in the general case of N>2 objectives, so let's just give the user a more detailed warning of what went wrong and what they should do about it.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.02 🎉

Comparison is base (1b86584) 96.60% compared to head (fd17331) 96.62%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #64      +/-   ##
==========================================
+ Coverage   96.60%   96.62%   +0.02%     
==========================================
  Files           8        8              
  Lines         795      801       +6     
==========================================
+ Hits          768      774       +6     
  Misses         27       27              

Impacted Files	Coverage Δ
src/MultiObjectiveAlgorithms.jl	93.50% <100.00%> (+0.17%)	⬆️
src/algorithms/DominguezRios.jl	100.00% <100.00%> (ø)
src/algorithms/KirlikSayin.jl	98.29% <100.00%> (ø)

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[remi-garcia]

KirlikSayin and DominguezRios do not use the nadir point but the anti-ideal point and an "estimation of the nadir point", respectively.

If the Pareto front is bounded, the nadir point (or an estimation of the nadir point) is also bounded. However the anti-ideal might not be.

In both implementations here, the anti-ideal point is computed hence the warning is necessary.