Rework case definition for better sum type support

[kurtmilam]

It should be possible to allow automatic expansion of cases based on sum types.

The new case definition might look like this for something other than a sum type:

Shape =
  { Circle: { Type: $.RecordType( { origin: Point, radius: $.ValidNumber } )
            , area: ( { radius } ) => Math.PI * radius * radius
            , move
            , move2
            } 
  }

With a little work ( marking the constructors, Types, standard and user-defined functions so they can be identified), the following should be a workable syntax for defining a case based on another sum type:

Shape =
  { Triangle }

Assuming Triangle is a sum type with two cases, Base and Equilateral, that should allow for syntax like:
Shape.Triangle.Base( { definition } ) and Shape.Triangle.Equilateral.Type, as well as for tagging a triangle correctly by passing it into Shape().

Shape.tags( equilateralTriangleDef ) could return [ 'Triangle', 'Triangle.Base', 'Triangle.Equilateral' ].