Release 0.27.0

Released 2023-01-17.
See also https://rasmus.krats.se/2023/rsass027.en
Progress: 4604 of 6925 tests passed.

• Changed repo structure to a monorepo (PR #164).
  • The commandline interface now lives in the separate crate rsass-cli.
  • The test updater also have a separate crate, but not intended for
    publication.
  • Tests are restructured to fail faster for simple things, while
    macos and windows testing is added to the github action (appveyor
    is removed).
• Added macros (PR #163, #165).
  • The workspace now includes a rsass-macros crate that can be used to
    compile sass to css strings at compile time in rust crates.
• Changed numeric handing (mainly conversions to/from f64) to match
  improvements in how dart-sass handles numerics. This is mainly done by
  removing some special cases as dart-sass and rust now agrees on more of
  those.
• Added new variables $epsilon, $max-safe-integer, $min-safe-integer,
  $max-number, and $min-number in sass:math, matching recent dart-sass
  additions.
• Added new split() function in sass:string module.
• Changed the span type used in parsing to a local type that borrows a
  SourceFile instead of nom_locate dependency (PR #158).
• Changed the type SourceFile to be reference counted, so cloned
  SourceFile objects share the same actual data (PR #158).
• Moved the SourcePos type into the input module and converted it from
  keeping a copy of the relevant line to keeping a range with a (reference
  counted) SourceFile (PR #158).
• Changed css creation from just writing to a text buffer to building
  a tree representation of the css (and serialize it to text as a
  final step) (PR #159).
• Changed BinOp value in both sass and css from a tuple variant with
  boxed values to a single boxed struct variant.
• Improved value checking; Report an error if trying to output invalid
  css values in some cases. Also, arithmetic involving colors that
  used to be calculated is now correctly invalid (PR #161).
• Changed css::Item::AtRule to wrap the new type css::AtRule.
• More varaints of Invalid, slightly fewer stringy errors.
• Changed handling of hue arguments to color functions, to allow
  different angle units, matching updates in sass-spec.
• Minor correctness improvent in the calc function handling.
• Clippy now takes MSRV from Cargo.toml. Slightly more recent lints allowed.
• Updated clap to 4.0 for the command-line interface.
• Updated sass-spec test suite to 2023-01-06.

Thanks to @Wicpar for the initial macros implementation.