* **Potentially breaking bug fix:** The argument name for the `saturate()`
function is now `$amount`, to match the name in LibSass and originally in Ruby
Sass.
* **Potentially breaking bug fix:** The `invert()` function now properly returns
`808080` when passed `$weight: 50%`. This matches the behavior in LibSass and
originally in Ruby Sass, as well as being consistent with other nearby values
of `$weight`.
* **Potentially breaking bug fix:** The `invert()` function now throws an error
if it's used [as a plain CSS function][plain-CSS invert] *and* the Sass-only
`$weight` parameter is passed. This never did anything useful, so it's
considered a bug fix rather than a full breaking change.
[plain-CSS invert]: https://developer.mozilla.org/en-US/docs/Web/CSS/filter-function/invert
* **Potentially breaking bug fix**: The `str-insert()` function now properly
inserts at the end of the string if the `$index` is `-1`. This matches the
behavior in LibSass and originally in Ruby Sass.
* **Potentially breaking bug fix**: An empty map returned by `map-remove()` is
now treated as identical to the literal value `()`, rather than being treated
as though it had a comma separator. This matches the original behavior in Ruby
Sass.
* The `adjust-color()` function no longer throws an error when a large `$alpha`
value is combined with HSL adjustments.
* The `alpha()` function now produces clearer error messages when the wrong
number of arguments are passed.
* Fix a bug where the `str-slice()` function could produce invalid output when
passed a string that contains characters that aren't represented as a single
byte in UTF-16.
* Improve the error message for an unknown separator name passed to the `join()`
or `append()` functions.
* The `zip()` function no longer deadlocks if passed no arguments.
* The `map-remove()` function can now take a `$key` named argument. This matches
the signature in LibSass and originally in Ruby Sass.