♻️ REFACTOR: Remove AttrDict

[chrisjsewell]

This is no longer used is core or mdit-py-plugins,
instead standard dictionaries are used.

[codecov]

Codecov Report

Merging #181 (9402c73) into master (934eb90) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #181      +/-   ##
==========================================
+ Coverage   96.08%   96.16%   +0.07%     
==========================================
  Files          61       61              
  Lines        3273     3259      -14     
==========================================
- Hits         3145     3134      -11     
+ Misses        128      125       -3     

Flag	Coverage Δ
pytests	96.16% <100.00%> (+0.07%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
markdown_it/common/utils.py	86.74% <ø> (+0.70%)	⬆️
markdown_it/common/entities.py	100.00% <100.00%> (ø)
markdown_it/rules_block/list.py	98.84% <100.00%> (ø)
markdown_it/rules_inline/entity.py	100.00% <100.00%> (ø)
markdown_it/utils.py	86.25% <100.00%> (+0.85%)	⬆️

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