Expose parser API as unstable

[pelletier]

This change exposes the internal parser as an unstable API.

It would allow people who don't mind trading off stability for the ability to access the AST produced by the parser.

Ref #822

@mikefarah let me know what you think!

[mikefarah]

Looks good to me! Can't comment too much till I actually try to use it of course :)

[mikefarah]

Hey @pelletier - how do I use the unstable API?

go get returns this error if I specify unstable:

go get github.com/pelletier/go-toml/v2/unstable

go: module github.com/pelletier/go-toml/v2@upgrade found (v2.0.5), but does not contain package github.com/pelletier/go-toml/v2/unstable

and if I just go get v2, then the unstable directory isn't there..

ls vendor/github.com/pelletier/go-toml/v2         
ci.sh  CONTRIBUTING.md  decode.go  doc.go  Dockerfile  errors.go  internal  LICENSE  localtime.go  marshaler.go  parser.go  README.md  scanner.go  SECURITY.md  strict.go  toml.abnf  types.go  unmarshaler.go  utf8.go

[pelletier]

I think this is because the unstable code has not been tagged yet, so go get defaults to the last tagged version, which does not include /unstable. You should be able to access it by specify the commit hash:

go get github.com/pelletier/go-toml/v2/unstable@94bd3ddcd650ed7a329f9f01c0b5926b8146b56a

I'll cut the release later today to simplify this for you.

[pelletier]

@mikefarah https://github.com/pelletier/go-toml/releases/tag/v2.0.6 there you go!