tr: .hydash and .hystop requests

The .hydash request specifies the list of characters after which words
may be broken (even when hyphenation is disabled) without inserting
hyphens.  Note that zero-width break point (\\:) is always in this
list.  The .hystop request specifies hyphenation inhibiting
characters.  Words containing any of the given characters are not
hyphenated, unless after dashes (characters specified via .hydash).