Environment Variables Misspelling

• Rename System.Etc.Internal.Util module to System.Etc.Internal.Extra
• Rename cabal flag from printer to extra
• Add feature for Environment Variable misspelling reports
• Add misspelling reports to example projects
• Improvements on README

Backwards compatibility

Adding support for previous versions of GHC (7.10.3 and 8.0.1)

• Various changes to source code to comply with previous resolvers
  • Use Monoid instead of Semigroup
  • Remove unused imports/typeclasses
• Bump upper limits for aeson and vector
• Improve README.md typos
• Add CHANGELOG

First release

Check main README for library overview