Documentation improvements

[mthh]

Just a few possible improvements that I noticed on my way through:

• The documentation of the proj4d3, unproject and project functions links to https://observablehq.com/@neocartocnrs/handle-geometries while the notebook actually speaking about these functions seems to be https://observablehq.com/@neocartocnrs/map-projections.

• The documentation of the tissot function links to a non-valid link (https://observablehq.com/@neocartocnrs/https://observablehq.com/@neocartocnrs/map-projections).

• The link to the issues in the documentation has a typo (see https://github.com/riatelab/geoviz/blob/main/jsdoc.json#L34).