v1.0.0a3: Fix dependency and GeometryField

• BUGFIX: Removed numpy as a dependency. This was causing issues with the installation of the package, since it was pinned to strictly. The dependency is not required, as shapely already has a dependency on numpy.;
• BUGFIX: When using the GeometryField it is now possible to instantiate the field with a the default shapely constructor. I.e. a MultiPolygon can be instantiated with a list of Polygon objects;