A class for generating an icosahedron geometry.
radius — Default is `1`.
detail — Default is `0`. Setting this to a value greater than `0` adds more
vertices making it no longer an icosahedron. When detail is greater than
1, it's effectively a sphere.
See the base [page:PolyhedronGeometry] class for common properties.
An object with a property for each of the constructor parameters. Any modification after instantiation does not change the geometry.
See the base [page:PolyhedronGeometry] class for common methods.
[link:https://github.com/mrdoob/three.js/blob/master/src/[path].js src/[path].js]