If the function the fiber is created from takes a parameter, the value
passed to the first call() or transfer() gets bound to that parameter.
Also, this now correctly handles fibers with functions that take
parameters. It used to leave the stack in a busted state. Now, it's a
runtime error to create a fiber with a function that takes any more
than one parameter.
- Break embedding out into a separate section with multiple pages.
- Document the constraints on the API.
- Document the slot array and WrenValue.
Still lots more to do, but getting there...
