Name what each class's instances are a pointer to - #124

A binding declares every wrapper in terms of the C type a class stands for, and
the catalog leaves that to the binding to work out — so each carries a map of
its own, and a class the model gains is one the binding cannot type until that
map is edited by hand. `classes.<Class>.cType` states it instead, over the 21 C
types MEOS's own signatures name.

It is read from those signatures rather than listed. A receiver-role method —
accessor, predicate, conversion, restriction, output — takes the value it is
called on first, so the pointee of that parameter names the type, and the
class's own methods answer for it. A class holding constructors alone says
nothing about itself that way: the concrete `<leaf><subtype>` classes take the
answer of the subtype they are a product of, `TFloatInst` reading `TInstant`
from `tinstant_*`, and any other class takes its parent's, which is the same C
type by construction. All 105 classes resolve one, and the nine the binding maps
by hand today — `Temporal`, `TInstant`, `TSequence`, `TSequenceSet`, `Set`,
`Span`, `SpanSet`, `TBox`, `STBox` — resolve to what that map says.

Three tests hold the three routes: the receiver, the subtype a constructor-only
class is a product of, and the parent a class with neither answers from.