Adding Axioms to a presentation

[jpfairbanks]

I was trying to write a test with a presentation of a finite group. But I am getting the following error.

@present D₄(ThGroup) begin
  (r,f) :: default

  (f⋅f) == e 
  (r⋅r⋅r⋅r) == e
end

Presentations: Error During Test at /Users/fairbanksj/github/AlgebraicJulia/Gatlab.jl/test/syntax/tests.jl:18
  Got exception outside of a @test
  LoadError: Bad comparison: f ⋅ f == e ⊣ [f]
  Stacktrace:
    [1] error(s::String)
      @ Base ./error.jl:35
    [2] fromexpr(ctx::GATlab.Syntax.GATs.GAT, e::Expr, #unused#::Type{GATlab.Syntax.Presentations.Presentation})
      @ GATlab.Syntax.Presentations ~/github/AlgebraicJulia/Gatlab.jl/src/syntax/Presentations.jl:68

[olynch]

Closed by #99