Dart-sass

* Fix a bug where `--watch` mode could go into an infinite loop compiling CSS
files to themselves.

* More aggressively eliminate redundant selectors in the `selector.extend()` and
`selector.replace()` functions.

Command Line Interface

* Fix a longstanding bug where `--watch` mode could enter into a state where
recompilation would not occur after a syntax error was introduced into a
dependency and then fixed.

* **Potentially breaking bug fix:** `use` rules whose URLs' basenames begin
with `_` now correctly exclude that `_` from the rules' namespaces.

* Fix a bug where imported forwarded members weren't visible in mixins and
functions that were defined before the `import`.

* Don't throw errors if the exact same member is loaded or forwarded from
multiple modules at the same time.

* Fix a bug where, under extremely rare circumstances, a valid variable could
become unassigned.

* Add functions to the built-in "sass:math" module.

* `clamp($min, $number, $max)`. Clamps `$number` in between `$min` and `$max`.

* `hypot($numbers...)`. Given *n* numbers, outputs the length of the
*n*-dimensional vector that has components equal to each of the inputs.

* Exponential. All inputs must be unitless.
* `log($number)` or `log($number, $base)`. If no base is provided, performs
a natural log.
* `pow($base, $exponent)`
* `sqrt($number)`

* Trigonometric. The input must be an angle. If no unit is given, the input is
assumed to be in `rad`.
* `cos($number)`
* `sin($number)`
* `tan($number)`

* Inverse trigonometric. The output is in `deg`.
* `acos($number)`. Input must be unitless.
* `asin($number)`. Input must be unitless.
* `atan($number)`. Input must be unitless.
* `atan2($y, $x)`. `$y` and `$x` must have compatible units or be unitless.

* Add the variables `$pi` and `$e` to the built-in "sass:math" module.

JavaScript API

* `constructor.value` fields on value objects now match their Node Sass
equivalents.