improved docs for core.Grid

[orbeckst]

• fix #69
• document all public attributes
• various text/syntax fixes
• fixed docs for MRC
• added forgotten import of mrc to core/init.py
• update CHANGELOG

[pep8speaks]

Hello @orbeckst! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file gridData/core.py:

Line 705:80: E501 line too long (83 > 79 characters) Line 744:80: E501 line too long (80 > 79 characters)

Comment last updated at 2022-02-21 05:03:35 UTC

[codecov[bot]]

Codecov Report

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

Project coverage is 88.08%. Comparing base (3129570) to head (683b9f7). Report is 32 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #106 +/- ## ========================================== + Coverage 88.07% 88.08% +0.01% ========================================== Files 6 6 Lines 855 856 +1 Branches 146 146 ========================================== + Hits 753 754 +1 Misses 60 60 Partials 42 42 ```

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[orbeckst]

Sorry, I don't know why RTD does not show up as a status check.

[IAlibay]

Just going to cycle the PR, sometimes "close and open" is enough to trigger webhooks.

[IAlibay]

There we go (unless @orbeckst did something in the background and "have you turned it on and off again" was just good timing :P )

[orbeckst]

thanks for the quick turnaround @IAlibay