Significant changes!

Name class renamed to Identity because it encompassed more than a simple name and "Name" was harder to find in the source.
Resolver.resolve returns false now when unable to resolve a module, instead of a module with source === false. The previous behavior was to allow modules resolved by the fallback to be cached by Needy. That's not necessary and creates extra side-effects that have to be handled.
Removed allowUnresolved option. It dependended on the resolver always returning a cached module even if the module couldn't really be resolved. It "could" still be allowed, always returning a new Object instance instead of throwing an exception, but it's complicated by fallback and the unresolved exports object wouldn't be persistant if the same unresolved module was resolved twice.
Added lib/identity and updated README.md
Updated version to v0.5.0