Read SDMX-CSV 2.0.0

[khaeru]

Closes #34.

PR checklist

• Checks all ✅
• Update documentation
• Update doc/whatsnew.rst

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.96%. Comparing base (70cf79c) to head (f70790d).
Report is 107 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #201      +/-   ##
==========================================
- Coverage   98.88%   97.96%   -0.92%     
==========================================
  Files          97       97              
  Lines        7861     8045     +184     
==========================================
+ Hits         7773     7881     +108     
- Misses         88      164      +76     

Files with missing lines	Coverage Δ
sdmx/model/common.py	99.90% <ø> (ø)
sdmx/model/v21.py	100.00% <ø> (ø)
sdmx/model/v30.py	100.00% <ø> (ø)
sdmx/reader/__init__.py	100.00% <100.00%> (ø)
sdmx/reader/csv.py	100.00% <100.00%> (ø)
sdmx/testing/__init__.py	99.35% <100.00%> (+<0.01%)	⬆️
sdmx/tests/reader/test_reader_csv.py	100.00% <100.00%> (ø)
sdmx/tests/test_model.py	100.00% <ø> (ø)
sdmx/tests/writer/test_csv.py	100.00% <100.00%> (ø)
sdmx/tests/writer/test_pandas.py	100.00% <100.00%> (ø)
... and 1 more

... and 18 files with indirect coverage changes