adopt NEP 29

[orbeckst]

• fix #102
• removed support for Python 2.7 and Python <3.8
  • removed six as dependency (setup.py and CI)
  • removed all from __future__ import ... statements
  • removed special Python division handling (and tests)
• update CHANGELOG
• set pip metadata to MATURE

[codecov[bot]]

Codecov Report

Merging #111 (b9b7314) into master (6fcf00e) will decrease coverage by 0.61%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #111      +/-   ##
==========================================
- Coverage   88.08%   87.47%   -0.62%     
==========================================
  Files           6        6              
  Lines         856      838      -18     
  Branches      146      146              
==========================================
- Hits          754      733      -21     
- Misses         60       62       +2     
- Partials       42       43       +1     

Impacted Files	Coverage Δ
gridData/CCP4.py	86.51% <ø> (-0.15%)	:arrow_down:
gridData/OpenDX.py	82.27% <ø> (-0.93%)	:arrow_down:
gridData/gOpenMol.py	86.11% <ø> (-0.38%)	:arrow_down:
gridData/mrc.py	96.77% <ø> (-0.20%)	:arrow_down:
gridData/core.py	94.18% <100.00%> (-0.22%)	:arrow_down:

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[orbeckst]

Also need to disable test requirement for dropped versions.

[orbeckst]

Done

[orbeckst]

Thanks @IAlibay i updated the metadata to show that we only support 3.8+.