class Protocol::HTTP::Headers

@parameter value [String] The raw header value.
@parameter key [String] The header key.
@parameter hash [Hash] The hash to merge into.

Merge the value into the hash according to the policy for the given key.

def merge_into(hash, key, value)
 = POLICY[key]
nt_value = hash[key]
_value << value
y] = policy.new(value)
't merge these, we only expose the last one set.
] = value