Hyoga: a Python library to visualize ice-sheet model datasets

This release removes the required dependency on cartopy by implementing own downloaders for Natural Earth and other (and future) data. All dependencies, and the docs, can be built with pip. Plot methods set aspect ratio to equal, and coordinate labels are hidden by default. Development has moved on a feature-branch squash workflow (as [xarray][https://xarray.dev) and geopandas).