Improve parsing and pretty printing of strings and lists

[Z-snails]

Pretty printing strings and lists is now iterative not recursive. Pretty printing strings uses escape characters Parsing strings accepts all escape characters expect for \u{XXXX} style escapes. I don't know if you want rust style \u{XXXX} or basically every other language style \uXXXX

[steinerkelvin]

Oh, I din't see this. I'll check out later.

[Z-snails]

The nix CI failing is an existing bug right? I hope I didn't cause it.

[steinerkelvin]

Yeah, it was already failing. I think I'll do something right now to at least disable it.

[steinerkelvin]

Ok, now the CI is passing, and is also running some test programs (/test/tests, #108) on HVM so we can be a bit more sure we aren't breaking anything.

@Z-snails please merge/rebase on master.

[Z-snails]

Hopefully I rebased this correctly