Add hyphenate breaks at hyphens

I recently used `hyphenation` to add soft hyphens to gwern.net so I could enable fully-justified text on desktop Chrome/Chromium browsers. (Bizarrely, for many years now, Chrome has had hyphenation on mobile Android but *not* desktop, and the devs have dragged their feet with the excuse that they just can't figure out how to ship dictionary files for desktop browsers; I gave up waiting for them to fix it.)

A user reported that [on Safari browsers](https://twitter.com/ctphoenix/status/1323036036813840384), Safari would line-break a hyphen-separated word like "compile-time" but there would be *two* hyphens: the original hyphen and then the smaller line-breaking hyphen, presumably the soft hyphen. Other browsers correctly ignore the soft hyphen and show only the regular hyphen if they need to line-break things like "compile-time". But why was there a soft hyphen there to begin with?

It turns out that `hyphenation` inserts soft hyphens even at existing hyphens!

~~~{.Haskell}
> H.hyphenate H.english_US "Compile-time"
["Com","pile-","time"]
~~~

I would expect instead a breaking like `["Com", "pile-time"]`. There is no need to insert a soft hyphen at the existing hyphen, since that is where a justification algorithm would break anyway. It can only cause problems, and in the case of Safari, does.

My current workaround is a post-processing hack to string-replace any hyphen+soft-hyphen present: `Data.Text.replace "-\173" "-"` etc. But this does other `hyphenation` users no good.

---

On an additional note, it would be nice to have a utility function which takes a String/Text and returns it with soft hyphens inserted. My current implementation goes like this, and it's complex enough that I'm not convinced I'm doing it right:

~~~{.Haskell}
T.pack $ unwords $ map (intercalate "\173" . H.hyphenate H.english_US{H.hyphenatorLeftMin=3}) $ words $ T.unpack s
~~~

(I don't know how much the lack of a native Text version hurts, but I'm sure it does my compile-times no good, anyway.)

Start by reproducing the H.hyphenate H.english_US example for “Compile-time” and inspect the hyphenation behavior around existing hyphens. The main change is done when no soft hyphen is inserted at an existing hyphen while normal break behavior remains intact; the optional String/Text utility request is a separate consideration.

Written by the indexing model from the issue text.