Better error messages for macros

[IainNZ]

So

@addConstraint(x <= 5)

is an error because there is no model (even though we could determine it, thats a different issue...)
But, due to Julia's poor line number error printing stuff, if this is in the middle of a largish function it won't tell you where, and won't even tell you what you've done wrong apart from an error about the wrong numbre of arguments.

Suggestion: make @addConstraint(x<=5) a valid macro that just throws an error saying to do it the "right" way.

[mlubin]

You can't overload macros based on the number of arguments, so this will make the code messier. Julia really needs to print a better error message in this case.

[IainNZ]

Oh really? Darn, thought I was being clever...

[mlubin]

Ref JuliaLang/julia#8701

[mlubin]

Upstream issue is resolved:

julia> @addNLConstraint(x <= 5)
ERROR: MethodError: `@addNLConstraint` has no method matching @addNLConstraint(::Expr)
Closest candidates are:
  @addNLConstraint(::ANY, ::ANY, ::Any...)

Not super user friendly but at least gives the name of the macro and a backtrace.