Implement population traits for Evaluated individual

[dbalcomb]

This implements additional traits for the Evaluated individual type.

The Evaluated individual, previously called Scored, was introduced as the default way to associated any individual with a separate fitness value. This allows users to use this type instead of writing a custom implementation of Individual which may need many different trait implementations to support all of the different operators. However, even Evaluated does not implement enough traits to be used everywhere. In particular it cannot be used with Generator::populate because although the inner genome may be a population the individual itself is not.

This change introduces new trait implementations for the Evaluated type to support the Populate generator. Specifically, this implements both Population and TryFromIterator. Various individuals such as Vec already implement both Individual and Population so this isn't anything new. The type is still primarily an individual but as the Population trait is used in place of a generic Collection trait it needs the implementation. The TryFromIterator trait is also a requirement of the Populate generator so it is also implemented.