More polymorphism in snapshot etc.

[dakom]

Currently, functions like snapshot allow passing in any type of Cell (i.e. CellLoop, CellSink, ...)

However, they must all be the same type right now. Need to change the signatures so that each kind gets its own type variable (e.g. SodiumCell celA, SodiumCell celB)

This isn't a showstopper since one can always use toCell to convert it

[clinuxrulz]

Sort of feels like implementing inheritance, and doing it the OO way. Which there is nothing wrong with in a FP language, it give convenience to the end user.