pub fn encode_word(text: &str) -> StringExpand description
Encode a header value as RFC 2047 encoded-words when it is not plain ASCII.
Headers are ASCII by definition, so Grüße has to travel as
=?UTF-8?B?R3LDvMOfZQ==?=. Long values become several encoded-words
separated by a fold, because one word may not exceed 75 characters.