Dart-sass

* Fix a bug where numbers could be written using exponential notation in
Node.js.

* Fix a crash that would appear when writing some very large integers to CSS.

Command-Line Interface

* Improve performance for stand-alone packages on Linux and Mac OS.

JavaScript API

* Pass imports to custom importers before resolving them using `includePaths` or
the `SASS_PATH` environment variable. This matches Node Sass's behavior, so
it's considered a bug fix.

* No user-visible changes.

* Support attribute selector modifiers, such as the `i` in `[title="test" i]`.

Command-Line Interface

* When compilation fails, Sass will now write the error message to the CSS
output as a comment and as the `content` property of a `body::before` rule so
it will show up in the browser (unless compiling to standard output). This can
be disabled with the `--no-error-css` flag, or forced even when compiling to
standard output with the `--error-css` flag.

Dart API

* Added `SassException.toCssString()`, which returns the contents of a CSS
stylesheet describing the error, as above.

* Allow `!` in `url()`s without quotes.

Dart API

* `FilesystemImporter` now doesn't change its effective directory if the working
directory changes, even if it's passed a relative argument.

* Avoid recursively listing directories when finding the canonical name of a
file on case-insensitive filesystems.

* Fix importing files relative to `package:`-imported files.

* Don't claim that "package:" URLs aren't supported when they actually are.

Command-Line Interface

* Add a `--no-charset` flag. If this flag is set, Sass will never emit a
`charset` declaration or a byte-order mark, even if the CSS file contains
non-ASCII characters.

Dart API

* Add a `charset` option to `compile()`, `compileString()`, `compileAsync()` and
`compileStringAsync()`. If this option is set to `false`, Sass will never emit
a `charset` declaration or a byte-order mark, even if the CSS file contains
non-ASCII characters.

* Explicitly require that importers' `canonicalize()` methods be able to take
paths relative to their outputs as valid inputs. This isn't considered a
breaking change because the importer infrastructure already required this in
practice.

* Consistently parse U+000C FORM FEED, U+000D CARRIAGE RETURN, and sequences of
U+000D CARRIAGE RETURN followed by U+000A LINE FEED as individual newlines.

JavaScript API

* Add a `sass.types.Error` constructor as an alias for `Error`. This makes our
custom function API compatible with Node Sass's.