Move the code for calling before hooks and the route handler to its own (private)
method. This will get wrapped by Return::MultiLevel to clean up forward/redirect
DSL methods.

As suggested in PerlDancer#432, use Return::MultiLevel to wrap route dispatch.
Cache the multilevel return coderef in the context for forward/redirect
to use.

Add Return::MultiLevel to prereqs and Scope::Upper to recommends.

Use the with_return handler to return immediatly to the dispatcher after the
redirect details have been added to the response.

Resolves PerlDancer#432.

…r forward.

This is the implementation of "... after a forward is executed, any remaining
code (route and hooks) from the current dispatch will never be run." from PerlDancer#432.

Include the description of forward and update that forward immediately
returns form the current route/hook. Update redirect docs to reflect
the immediate return from route/hook.