Add ciris-generic module using shapeless

[vlovgr]

Support for loading shapeless' coproducts and products with arity 1 (including value classes).

[codecov]

Codecov Report

Merging #9 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master     #9   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          19     20    +1     
  Lines         305    323   +18     
  Branches        1      1           
=====================================
+ Hits          305    323   +18

Impacted Files	Coverage Δ
...ore/shared/src/main/scala/ciris/ConfigReader.scala	100% <100%> (ø)	⬆️
...a/ciris/generic/readers/GenericConfigReaders.scala	100% <100%> (ø)
...core/shared/src/main/scala/ciris/ConfigError.scala	100% <100%> (ø)	⬆️

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