plan for ImodModel creation API and point2model function

[alisterburt]

following from discussion in #24 here is a proposed API that will simplify creation of ImodModels for writing out with the new imodmodel.write() function (thanks @jojoelfe !)

• Contour.from_numpy(arr: np.ndarray)
• Object.from_contours(contours: list[Contour])
• ImodModel.from_objects(objects: list[Object])

We also want a convenience API available at the top level of imodmodel for creating models

• imodmodel.point2model(points: np.ndarray) -> ImodModel

@uermel suggested he may find time to implement this in the near future