Version 3.0 of XTGeo!

What's Changed

Drop support for Python 3.6. Python 3.7 to 3.11 are supported.
As a consequence of skipping Python 3.6, Python in RMS 12.0 (Roxar API version 1.4) and earlier is not supported from this version.
Functions and methods with deprecation warnings marked for removal in xtgeo 3.0 are now removed. These are:
- Grid() class: numpify_carrays(), get_cactnum(), get_indices()
- BasePlot() class: set_colortable()
- RegularSurface() class: get_zval(), set_zval(), ensure_correct_values(), use of nx, ny in class instantiating (use ncol, nrow instead)

Full Changelog: 2.21.3...3.0.0