hex_bw() function and integration into gglikert()

[larmarange]

fix #57

• [x] add tests
• [x] update NEWS

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.30%. Comparing base (86740a8) to head (d60d194). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #58 +/- ## ========================================== + Coverage 96.11% 96.30% +0.18% ========================================== Files 12 14 +2 Lines 1134 1190 +56 ========================================== + Hits 1090 1146 +56 Misses 44 44 ```

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