adopt SPEC 0 instead of NEP 29

[orbeckst]

• fix #369
• once this is fixed, we can update the JOSS paper draft PR #328 to only mention SPEC 0

[codecov[bot]]

Codecov Report

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

Project coverage is 98.83%. Comparing base (6f403f4) to head (bd650af). Report is 9 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #370 +/- ## ======================================= Coverage 98.83% 98.83% ======================================= Files 28 28 Lines 1895 1895 Branches 407 407 ======================================= Hits 1873 1873 Misses 2 2 Partials 20 20 ```

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