Release v0.38.0

## Maintenance:

- Update module and CI dependencies.
- Clean up documentation and README.

## Feature:

Add handler.Struct. This is a wrapper for handler.Check for the special case of
a function with a single non-context argument of a struct type (or a pointer to
struct). The generated wrapper accepts its arguments as an object or an array
(as handler.Positional), but the field names are derived from the struct rather
than supplied by the caller.