Previously, templates were used in the implementation of CastAndCall to
find the type and call the underlying function. The templates checked
one type at a time.
However, compilers were not always great at optimizing a 15-call deep
stack with an if statement at each one. Instead, use a case statement in
a single function block. This requires providing separate code for each
number of types. Currently, up to 20 are created (with pyexpander). If
there are more than that, then the template recurses.
