Add syntax for Parameter

[odow]

Still a WIP. Got distracted by #3442

Part of #1185

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01% 🎉

Comparison is base (27213d3) 97.99% compared to head (71b3f5f) 98.00%.
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3443      +/-   ##
==========================================
+ Coverage   97.99%   98.00%   +0.01%     
==========================================
  Files          36       36              
  Lines        5041     5068      +27     
==========================================
+ Hits         4940     4967      +27     
  Misses        101      101              

Files Changed	Coverage Δ
src/macros.jl	98.67% <100.00%> (+<0.01%)	⬆️
src/sets.jl	100.00% <100.00%> (ø)
src/variables.jl	99.00% <100.00%> (+0.03%)	⬆️

... and 1 file with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[joaquimg]

What about a macro:
@parameter(model, x == 2)

It would be more natural for beginners to create a parameter instead of a variable constrained in the parameter set.

[blegat]

It would be more natural for beginners to create a parameter instead of a variable constrained in the parameter set.

We already have @variable(model, x in ComplexPlane()) and no @complex(model, x). Using the @variable macro might be more consistent with the rest.

[odow]

Any other comments?