Updating README to refer to ANTLR 5

[ftomassetti]

I took a first look at the README, renaming most references to ANTLR 4 into references to ANTLR 5.

I also tried to:

• State that this project is experimental, and that most people should look at ANTLR 4
• Summarizing very shortly why ANTLR 5 came to by and pointing out to antlr5-specs for the details
• Remove some links that were very specific to ANTLR 4
• Add a comment about The Definitive ANTLR 4 Reference, in the context of ANTLR 5
• Add a reference to grammars-v5 (while keeping a reference to grammars-v4)

This is related to #3

Follow up: Update image to change master into main. This would be easier if we had the sources of the image.

[ericvergnaud]

Thanks! I'm fine with the proposed changes, but @KvanTTT has asked to put on hold any PR until he completes #6 so I'll merge once done.

[ftomassetti]

Makes sense, thank you Eric!

[sschuberth]

put on hold any PR until he completes #6 so I'll merge once done.

That PR doesn't touch the README.md, though... yet.

[ericvergnaud]

Sure but he might need to rebase to an old commit, in which case we'd have to redo all this...
Let's be patient, it looks like we're not very far...

[kaby76]

The phrase "without actions" has bothered me for a while. I don't think it is correct.

First, there are many grammars in grammars-v4 that contain both "actions" and "semantic predicates". According to the documentation:

• "Actions are blocks of text written in the target language and enclosed in curly braces. The recognizer triggers them according to their locations within the grammar."

• "Semantic predicates, {...}?, are boolean expressions written in the target language that indicate the validity of continuing the parse along the path "guarded" by the predicate."

In either case, we have a slew.

• "actions", using Trash, //actionBlock[not(following-sibling::QUESTION)].
  actions.txt

• "semantic predicates", using Trash, //actionBlock[following-sibling::QUESTION].
  sem-preds.txt

Secondly, they are lexed identically, and parsed nearly identically.

The phrase should be deleted.

[ftomassetti]

Thank you, I will remove the sentence

[KvanTTT]

@ftomassetti please rebase on dev and remove duplicated commit (78a857c).

[KvanTTT]

That PR doesn't touch the README.md, though... yet.

Yes, but I want to keep git history as clear as possible. Maybe it's out of priority for other contributors but it's important for me (I've been working on Kotlin Compiler for almost 3 years and I understand how it could be important). That's why I adhere Rebase and merge or Squash and merge merging methods that don't produce extra merging commits.

And I didn't want to have extra commits in dev before #6 merging (I can't interactively rebase that branch because it is non-standard since it contains merge from unrelated histories). Yes, I could use commits cherry-picking, but it was better to wait until merging.

Now the merge is finished (force-push to dev) and other PRs can be merged using safe GitHub methods.

[ftomassetti]

I know I need to re-sign the commits, but I am currently at a computer where I need to reconfigure GPG, so I will do that as soon as I can

[ftomassetti]

Ok, it seems now that DCO and tests are all green

[ericvergnaud]

I suggest you rebase, I had some changes on my side not yet merged.

[ftomassetti]

Sure, I have now rebased

[ftomassetti]

Thank you for approving the PR!
I think I cannot merge this myself, so would you merge it?
I see there is also a check failing (regarding the kotlin runtime but only on macos). However, given I just touched the README, I think we can safely consider it unrelated to the PR