Bump to 5.1.0

[Enselic]

Draft of release notes:

Improvements

• Fix how syntect::util::split_at() handles multi-byte characters
• Allow case insensitive search for .tmtheme paths
• impl PartialEq for Theme

Dependencies

• Upgrade fancy-regex to 0.11
• Upgrade regex-syntax to 0.7
• Replace lazy_static with once_cell

Other

• Change MSRV policy to "last three stable versions"
• Make Debug impl of syntect::highlighting::Color less verbose

(I have confirmed that this version of syntect passes all bat regression tests: sharkdp/bat#2632)

[Enselic]

Note: Strictly speaking this should be 6.0.0 because we remove public API, but we have previously decided to take the risk. See #438 (review) and the rest of the discussion for details.

[trishume]

Thanks for putting this together!

[trishume]

How about you try doing the release yourself and let me know if you run into any permissions snags.

[Enselic]

Sounds good! Will try.

[Enselic]

Went smoothly! (knock on wood)