Some experiments allowing other types of index
New type definition, separated constructors, experiment with symbols as index
Intermediate.  I'll have to re-think my constructors---this is going nowhere.
Simplified constructors, re-ordering type, names and dimnames now tuples, passing test.jl
More support for non-string names.
Reordered constructors, now DT in type is no longer VarType but concrete type.  Type check in setnames!