DEV: Fix flake8 issues and add pre-commit

[scottclowe]

No description provided.

[codecov]

Codecov Report

Merging #217 (c60243e) into master (0829998) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master     #217   +/-   ##
=======================================
  Coverage   93.23%   93.23%           
=======================================
  Files           8        8           
  Lines         916      916           
  Branches      184      184           
=======================================
  Hits          854      854           
  Misses         32       32           
  Partials       30       30           

Flag	Coverage Δ
nbsmoke	66.70% <0.00%> (ø)
unittests	92.79% <0.00%> (ø)

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Impacted Files	Coverage Δ
fissa/ROI.py	78.26% <ø> (ø)
fissa/deltaf.py	100.00% <ø> (ø)
fissa/readimagejrois.py	91.34% <0.00%> (ø)
fissa/roitools.py	90.22% <0.00%> (ø)

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