Add some writers

Can all go right from `xr.DataArray`. Should not need a class.

Targets:

- CSV
- NetCDF/HDF5
- NumPy?
- GeoJSON
- GeoTIFF
- PNG?
- SHP?
- GPKG
- DEM? E00

Should probably be able to write to formats we read?

- OdT horizon
- ZMAP+ (is in `zmapio`, also GeoJSON)
- Surfer 6
- Surfer 6 ASCII
- Surfer 7

All the formats: https://gisgeography.com/gis-formats/