Update Python packaging

[khaeru]

• Move content from setup.py to setup.cfg.
• Use setuptools-scm to set the package version based on tags.

[codecov]

Codecov Report

Merging #26 into master will not change coverage.
The diff coverage is 33.33%.

@@           Coverage Diff           @@
##           master      #26   +/-   ##
=======================================
  Coverage   49.96%   49.96%           
=======================================
  Files          33       33           
  Lines        1507     1507           
=======================================
  Hits          753      753           
  Misses        754      754           

Impacted Files	Coverage Δ
item/tests/test_historical.py	0.00% <0.00%> (ø)
item/remote/sdmx.py	100.00% <100.00%> (ø)

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