Minor readability and code enhancments

[Hexoplon]

Fixes introduced based on golangci-lint using the --enable-all flag

[codecov-io]

Codecov Report

Merging #4 into master will decrease coverage by 1.41%. The diff coverage is 86.36%.

@@            Coverage Diff            @@
##           master      #4      +/-   ##
=========================================
- Coverage   87.02%   85.6%   -1.42%     
=========================================
  Files           2       2              
  Lines         131     132       +1     
=========================================
- Hits          114     113       -1     
- Misses         11      12       +1     
- Partials        6       7       +1

Impacted Files	Coverage Δ
filemetadata.go	100% <100%> (ø)	:arrow_up:
exiftool.go	71.21% <57.14%> (-2.64%)	:arrow_down:

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[Hexoplon]

@barasher Reverted to using constants while maintaining the minor enhancments. Renamed PR title

[barasher]

Thanks for the PR :)