Using the bullet for unnamed objects

[jpfairbanks]

When defining a diagrammatic equation, we want to use the bullet character to denote all the intermediate variables. Julia does not approve:

julia> @present P(FreeCategory) begin
       •::Ob
       end
ERROR: syntax: invalid character "•" near column 1
Stacktrace:
 [1] top-level scope
   @ none:1

Unless...

julia> @present P(FreeCategory) begin
       var"•"::Ob
end