Add a few text-related generators

[voidus]

Based on my fumbling at #52 I added this to my project and thought if might be something you'd want to include.

The code points are taken from Hedgehog. I did consider adjusting the weights of unicode to skew more towards printable characters, but theres a lot of codepoints in unicde and I thought it's better to have hex escape codes than being biased too much towards ascii or sth.

I'm not sure what an appropriate level of testing for code like this would be. I'd be happy to add some, but I think I need a little guidance on what to test.

This PR builds on #54 , if you're interested in merging this one but are concerned about chooseAny, let me know and I'll remove the dependency

[edsko]

This all looks reasonable enough to me. Some suggestions:

• Rather than making this part of the standard generators exported by .Generator, we make this a dedicated module; probably we don't want to pollute the general namespace with all kinds of text related generators (I suspect over time more might be added)
• I have no problem with the dependency on Add chooseAny, a version of choose that takes NonEmpty (Gen a) #54 (which I've merged but renamed chooseAny to oneof), but let's avoid the nix stuff if we can (there are some flake files added in this PR).
• In terms of testing, I would let say, let's add a few tests to TestSuite/Prop/Generator, maybe a few shrinking tests or minimal value tests for some of these generators. Having a few checks in there will already prevent a lot of regressions, doesn't have to be anything particularly fancy.

[edsko]

Thanks for the contribution!

[edsko]

(I do like the "shrink towards printable" goal you mentioned in #52; that is something we can write a test for.)

[voidus]

rebased out the accidentally commited flake.{nix,lock}, I'll look into the other comments when I find time

[voidus]

I reworked stuff a little and added tests. (They found issues of course 😃)

Still need to have a short think of how to best test string and text, will look into that later.

[edsko]

Marked this as WIP. Feel free to ping me when you think this is ready for review :)