Feature VectorAffineFuncton in AllDifferent/Table

[Wikunia]

Closes #235

It was only possible to have a vector of variables to be alldifferent or part of a TableSet constraint. Sometimes as pointed out by @hakank it makes sense however to support things like [x[i] + i for i in 1:4] in CS.AllDifferentSet().

This internally works as follows:

• each affine function which isn't directly a variable will create a new variable and a linear equalto constraint
• i.e [x[i] + i for i in 1:4] in CS.AllDifferentSet() will be

  # xip a vector of 4 variables
  for i in 1:4
  @variable(model, lb <= xip[i] <= ub, Int) # the lower and upper bound are getting computed
  @constraint(model, xip[i] == x[i]+i)
  end
  @constraint(model, xip in CS.AllDifferentSet())

  the same can be done with TableSet and it also allows to not have normal affine functions like the one above but also just simple integer constants which was the first part of issue #235

[codecov[bot]]

Codecov Report

Merging #268 (b4749f8) into master (80a6050) will increase coverage by 0.06%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #268      +/-   ##
==========================================
+ Coverage   97.53%   97.60%   +0.06%     
==========================================
  Files          53       53              
  Lines        4428     4469      +41     
==========================================
+ Hits         4319     4362      +43     
+ Misses        109      107       -2     

Impacted Files	Coverage Δ
src/MOI_wrapper/constraints.jl	99.59% <100.00%> (+0.04%)	:arrow_up:
src/MOI_wrapper/util.jl	100.00% <100.00%> (ø)
src/ConstraintSolver.jl	99.14% <0.00%> (+0.56%)	:arrow_up:

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[Wikunia]

I should make sure that only integer constants and probably coefficients are used. Not sure whether I should disallow it or just warn when it happens though. As an example

[x,1.5y] in CS.TableSet([1,3;])

Could make sense somehow but

[x,1.5y] in CS.AllDifferentSet()

should in principle give a solution to y=1 but the newly created variable 1.5y is integer as the solver doesn't allow continuous variables.