Support 'turn' unit for <angle>
In addition to deg
, rad
, and grad
, the CSS Values and Units Module Level 3 now also supports turn
as a unit for angles: https://www.w3.org/TR/css3-values/#angles
Adding this should just be a matter of adding another line to the parser and to the tests. E.g. 1turn
should be equivalent to 360deg
.