Add pre-commit hooks

[zakajd]

Closes #271

Proposed Changes

• Add pre-commit config and setup guide
• Format all files according to it
• Fix spelling issues

@snk4tr you wanted to do this yourself, but I'm just tired of formatting files by hand 😄 This should eliminate "Fix flake8" and "Fix mypy" commits entirely.

Ready for review. It seems like a lot of files have changed, but it's mostly whitespace difference.

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov[bot]]

Codecov Report

Merging #293 (b767ad9) into master (6e06c80) will decrease coverage by 2.27%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #293      +/-   ##
==========================================
- Coverage   93.27%   91.00%   -2.28%     
==========================================
  Files          33       33              
  Lines        2289     2289              
==========================================
- Hits         2135     2083      -52     
- Misses        154      206      +52     

Flag	Coverage Δ
unittests	91.00% <100.00%> (-2.28%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
piq/base.py	88.46% <ø> (ø)
piq/dss.py	98.96% <ø> (ø)
piq/fsim.py	100.00% <ø> (ø)
piq/functional/base.py	92.10% <ø> (ø)
piq/functional/colour_conversion.py	100.00% <ø> (ø)
piq/functional/resize.py	67.14% <ø> (ø)
piq/gmsd.py	100.00% <ø> (ø)
piq/gs.py	32.96% <ø> (-57.15%)	:arrow_down:
piq/haarpsi.py	100.00% <ø> (ø)
piq/mdsi.py	100.00% <ø> (ø)
... and 13 more