Introduce Codec.codecForEnumeration, add tests, change error slightly

[travisbrown]

I've added laws-checking for these instances, which turned up the fact that on decoding failures we were passing along the whole NoSuchElementException stack trace, which seems kind of bad, so I fixed it.

[codecov-io]

Codecov Report

Merging #1232 into master will decrease coverage by 0.09%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #1232     +/-   ##
=========================================
- Coverage   86.55%   86.46%   -0.1%     
=========================================
  Files          92       92             
  Lines        2841     2859     +18     
  Branches      123      119      -4     
=========================================
+ Hits         2459     2472     +13     
- Misses        382      387      +5

Impacted Files	Coverage Δ
...es/core/shared/src/main/scala/io/circe/Codec.scala	64% <100%> (+64%)	⬆️
.../core/shared/src/main/scala/io/circe/Decoder.scala	85.32% <100%> (-0.18%)	⬇️
.../core/shared/src/main/scala/io/circe/Encoder.scala	89.28% <100%> (ø)	⬆️
...les/core/shared/src/main/scala/io/circe/Json.scala	78.04% <0%> (-1.83%)	⬇️
...re/shared/src/main/scala/io/circe/JsonNumber.scala	96.38% <0%> (-1.21%)	⬇️
...rc/main/scala/io/circe/numbers/BiggerDecimal.scala	84.21% <0%> (-0.59%)	⬇️
...re/shared/src/main/scala/io/circe/KeyDecoder.scala	97.29% <0%> (+2.7%)	⬆️

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