Feat unicode softhyphen support

[Omikhleia]

Closes #1930

The proposal described there, with a test.

[alerque]

Any thoughts on a release target for this? v0.14.14? v0.15.0? Let it simmer?

[Omikhleia]

@alerque

Any thoughts on a release target for this? v0.14.14? v0.15.0? Let it simmer?

If deemed acceptable, both #1935 and #1918 (EDIT) need proper documentation and could eventually go in 0.15 -- There's no real urge for them, your call depending on your release schedule!

[Omikhleia]

Removed the "Draft" by the way. Looking at the expected results, I realized we could do better (avoiding the string to be split in multiple unshaped tokens when soft hyphens are ignored = so ligatures will work then) and I rebased my earlier version.

[alerque]

I definitely approve of the direction and as much of the implementation as I see, so document away. Since it isn't a breaking change I'm totally fine with putting it in the next minor release (semver patch level). I'll keep making those occasionally until such a time as v0.15.0 is ready. That still has a bit of baking to do but I'm hoping it won't be too much longer.

[Omikhleia]

Documentation added in the manual ch. 8, "Hyphenation" section, as a note.