Spell-check documentation

[khaeru]

PR checklist

• [x] Checks all ✅
• [x] Update documentation
• ~Update doc/whatsnew.rst~ N/A

[codecov[bot]]

Codecov Report

Merging #136 (65c9048) into main (92254d8) will decrease coverage by 2.23%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #136      +/-   ##
==========================================
- Coverage   98.26%   96.03%   -2.23%     
==========================================
  Files          82       82              
  Lines        6334     6334              
==========================================
- Hits         6224     6083     -141     
- Misses        110      251     +141     

Files Changed	Coverage Δ
sdmx/model/common.py	99.89% <ø> (ø)

... and 16 files with indirect coverage changes