each with default html for empty

[charleso]

eachOr : List a -> Html -> (a -> Html) -> Html

Naming open to suggestion

[thumphries]

Requires one of

• implementing first class lists (eh, not worth it just for this)
• allowing pattern matching on lists (might require care to make this work with purs arrays)
• adding a primitive equivalent to L.null plus if

[thumphries]

Can be implemented trivially as a library function once we have #221