Use constant names, Help the compiler detect value changes

[dmarkham]

After reading dominikh/go-tools#660 and alvaroloes/enumer#59

I Like the ideas and have put together something that address the issues.

[codecov-io]

Codecov Report

Merging #30 into master will increase coverage by 0.92%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #30      +/-   ##
==========================================
+ Coverage   65.21%   66.14%   +0.92%     
==========================================
  Files           3        3              
  Lines         437      449      +12     
==========================================
+ Hits          285      297      +12     
  Misses        140      140              
  Partials       12       12

Impacted Files	Coverage Δ
enumer.go	100% <100%> (ø)	⬆️
stringer.go	61.22% <100%> (+1.22%)	⬆️

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[dmarkham]

@domsekotill I used your suggestion to build in the compile time check, I did not need to modify it that much to get it passing all the tests. Very slick idea 👍