Add forEachWithIndex to Array

[benrimmington]

Instead of foo.enumerated() you might want to use:

1. zip(0..., foo) or
2. zip(foo.indices, foo)

See also:

• [Idea] Add an (Index, Element) sequence to CollectionType

• [Idea] Replace enumerate() with something more explicit

• Removing enumerated?

• [Pitch] Enumerate from offset