update build sytem to pyproject.toml

[larsbuntemeyer]

updates of build system (setuptools is deprecated):

• using pyproject.toml file instead of setup.py
• using setuptools_scm for automatic updating of version numbers.
• updates for pre-commit

[codecov-commenter]

Codecov Report

Merging #40 (42812bb) into master (da8b6b8) will decrease coverage by 2.29%.
Report is 2 commits behind head on master.
The diff coverage is 75.00%.

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@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
- Coverage   94.79%   92.51%   -2.29%     
==========================================
  Files          14       14              
  Lines        1268     1282      +14     
==========================================
- Hits         1202     1186      -16     
- Misses         66       96      +30     

Flag	Coverage Δ
unittests	92.51% <75.00%> (-2.29%)	⬇️

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Files	Coverage Δ
index_calculator/__init__.py	93.54% <75.00%> (-6.46%)	⬇️
index_calculator/_ci_netcdfattrs.py	91.93% <75.00%> (-2.61%)	⬇️

... and 2 files with indirect coverage changes