We don't support unnamed arguments, and we give a terrible error
("Parameter has an unsupported type.") when you use them.

They're very simple to implement so we should just do it.

This will simplify potentially adding annotations for them in #545.

Fixes #554

A u32 bitflags structure should allow a 1<<31 value. However, with
current cbindgen this produces a compiler error with latest clang, because
1<<31 is treated as a signed value (-2147483648) which cannot be narrowed
back into a uint32_t without a cast.

This fixes the scenario by adding an explicit cast based on type
of the field.

Fixes #555

…an be inferred from the Rust type.

…iant.

There should be no behavior change.

There are two situations where we can legitimately end up with a
different number of template params.

Fixes #532.
Fixes #527.