Improvements

[scorphus]

• Update submodule reference
• Add new run target to Makefile
• Update license year span
• Add missing file header
• Determine transparency based on alpha channel and its minima
• Set specific SSIM precision for certain tests
• Drop support to Python 3.6

[codecov-commenter]

Codecov Report

Merging #11 (f7c35ff) into main (2b853ad) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #11   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines           74        77    +3     
=========================================
+ Hits            74        77    +3     

Impacted Files	Coverage Δ
thumbor_wand_engine/__init__.py	100.00% <ø> (ø)
thumbor_wand_engine/engine.py	100.00% <100.00%> (ø)

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