class val Header
"""
A single HTTP header name-value pair.
Used by `Headers.values()` to iterate over header entries. Names are
lowercased by `Headers` on storage, so `name` will always be lowercase.
"""
let name: String val
let value: String val
new val create(name': String val, value': String val) =>
"""Create a header with the given name and value."""
name = name'
value = value'