Added pre-commit hooks

[marksweb]

This adds the following pre-commit hooks;

• pyupgrade
• django-upgrade
• flake8
• yesqa
• check-merge-conflict
• mixed-line-ending
• isort

[codecov-commenter]

Codecov Report

Merging #111 (7571e95) into master (a650d08) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 7571e95 differs from pull request most recent head 01e8e17. Consider uploading reports for the commit 01e8e17 to get more accurate results

@@           Coverage Diff           @@
##           master     #111   +/-   ##
=======================================
  Coverage   96.71%   96.71%           
=======================================
  Files           6        6           
  Lines         213      213           
  Branches       44       44           
=======================================
  Hits          206      206           
  Misses          4        4           
  Partials        3        3           

Impacted Files	Coverage Δ
sekizai/helpers.py	95.83% <100.00%> (ø)
sekizai/templatetags/sekizai_tags.py	100.00% <100.00%> (ø)

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