Prepare for 5.0.0: Update CHANGELOG.md and version

[Enselic]

Update CHANGELOG.md and bump version to 5.0.0 to make it as easy as possible to release 5.0.0 later when we feel ready (let's again wait a few days at least before we make the release).

The only known thing left to do is to update the 5.0.0 release date in CHANGELOG.md to the date when the release is made.

The updated CHANGLOG.md includes entries for the following open PRs:

• For 5.0.0: Rename HighlightLines::highlight() to highlight_line() #406
• For 5.0.0: Bring back plist-load feature #407
• For 5.0.0: Remove obsolete dump-load-rs and dump-create-rs features #408
• For 5.0.0: Remove all deprecated items #411

[Enselic]

FWIW, here is all bat regression tests passing with all above open PRs merged to a single temporary branch and used in bat: https://github.com/Enselic/bat/actions/runs/1650806678 (from Enselic/bat#85)

Since both syntect CI and bat CI is green for the 5.0.0 changes, it should be safe to at least merge these PRs to syntect git master if they look good code-review-wise. Once they are merged we (read: I) can do additional verification before we publish 5.0.0. Third time's a charm... 🤞

[Enselic]

These are probably/potentially easy to fix but semver breaking, so I'd like to look into these too before we release 5.0.0:

• Implement Error trait for error types #94 (see Implement Error and Display for all error enums by using thiserror #420)
• Replace calls to panic! with Result types #98
• Separate feature for theme/syntax bundling #310 (see For 5.0.0: Split up feature assets into default-syntaxes and default-themes #417)
• RUSTSEC-2020-0159 #385 (see Bump plist to 1.3.0 #414)
• discover_theme_paths doesn't follow symbolic links #396 (see Follow symbolic links when walking directories #415)
• Add some #[non_exhaustive] so we can make fixes like Fall back to "Plain Text" if embeds are missing Enselic/syntect#6 without a major bump (see For 5.0.0: ContextReference: Mark as #[non_exhaustive] #416)

[trishume]

I did a pass over all the PRs with just some comments on making the upgrade path smoother.

[trishume]

Alright, merged all the open 5.0 PRs, if you want to release now just do any changelog updates and ping me and I'll merge this and release. If you still want to do the Error thing that sounds good to me and I'll wait for that.

[Enselic]

Thanks for all reviews!

I just created a PR to fix the Error thing: #420.

Once that PR has landed I also would like to at least make highlight_line return a Result for #98. I have done some prototyping and it seems pretty straightforward, but I'd like the Error PR to land first.

Once that is done I think we have a pretty solid and future proof API for a 5.0.0 release, and will be happy to update CHANGELOG.md.

[Enselic]

Just wanted to give an update. I just created #432 that I believe is the last change we should land before we make a 5.0.0 release.

So if all goes according to plan, we will

1. Review and merge that PR
2. I will update this PR, which we then merge
3. We then make a syntect v5.0.0 release

[Enselic]

I have now updated this PR to include the changes in master and #432. So after

• Replace direct panics with Errors #432 and
• Prepare for 5.0.0: Update CHANGELOG.md and version #409

have been merged, we should be able to release syntect 5.0.0. What could go wrong, right? ;)

I have verified that all regression tests in bat passes in a build with those two PRs included: https://github.com/Enselic/bat/actions/runs/2084215734

[Enselic]

Merging since #432 was just merged