Dart-sass

* Properly merge `all and` media queries. These queries were previously being
merged as though `all` referred to a specific media type, rather than all
media types.

* Never remove units from 0 values in compressed mode. This wasn't safe in
general, since some properties (such as `line-height`) interpret `0` as a
`<number>` rather than a `<length>` which can break CSS transforms. It's
better to do this optimization in a dedicated compressor that's aware of CSS
property semantics.

* Match Ruby Sass's behavior in some edge-cases involving numbers with many
significant digits.

* Emit escaped tab characters in identifiers as `\9` rather than a backslash
followed by a literal tab.

Command-Line Interface

* The source map generated for a stylesheet read from standard input now uses a
`data:` URL to include that stylesheet's contents in the source map.

Node JS API

* `this.includePaths` for a running importer is now a `;`-separated string on
Windows, rather than `:`-separated. This matches Node Sass's behavior.

Dart API

* The URL used in a source map to refer to a stylesheet loaded from an importer
is now `ImportResult.sourceMapUrl` as documented.

Node JS API

* When `setValue()` is called on a Sass string object, make it unquoted even if
it was quoted originally, to match the behavior of Node Sass.

* Always add quotes to attribute selector values that begin with `--`, since IE
11 doesn't consider them to be identifiers.

* Add support for passing arguments to `content` blocks. See [the
proposal][content-args] for details.

* Add support for the new `rgb()` and `hsl()` syntax introduced in CSS Colors
Level 4, such as `rgb(0% 100% 0% / 0.5)`. See [the proposal][color-4-rgb-hsl]
for more details.

* Add support for interpolation in at-rule names. See [the
proposal][at-rule-interpolation] for details.

* Add paths from the `SASS_PATH` environment variable to the load paths in the
command-line interface, Dart API, and JS API. These load paths are checked
just after the load paths explicitly passed by the user.

* Allow saturation and lightness values outside of the `0%` to `100%` range in
the `hsl()` and `hsla()` functions. They're now clamped to be within that
range rather than producing an error if they're outside it.

* Properly compile selectors that end in escaped whitespace.

[content-args]: https://github.com/sass/language/blob/master/accepted/content-args.md
[color-4-rgb-hsl]: https://github.com/sass/language/blob/master/accepted/color-4-rgb-hsl.md
[at-rule-interpolation]: https://github.com/sass/language/blob/master/accepted/at-rule-interpolation.md

JavaScript API

* Always include the error location in error messages.

* Properly escape U+0009 CHARACTER TABULATION in unquoted strings.

* Treat `:before`, `:after`, `:first-line`, and `:first-letter` as
pseudo-elements for the purposes of `extend`.

* When running in compressed mode, remove spaces around combinators in complex
selectors, so a selector like `a > b` is output as `a>b`.

* Properly indicate the source span for errors involving binary operation
expressions whose operands are parenthesized.