Update CHANGELOG with new igl functions

Add missing igl functions to support dropping igl dependency.

Author: jf---

CHANGELOG.md

@@ -9,6 +9,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+Add missing igl functions to enable `compas_slicer` to drop the `igl` dependency entirely:
+
+- cotmatrix module: trimesh_cotmatrix, trimesh_cotmatrix_entries
+- grad module: trimesh_grad (gradient operator)
+- meshing module: trimesh_cut_mesh, trimesh_face_components
+- simplify module: ramer_douglas_peucker (polyline simplification)
+
 ### Changed
 
 ### Removed