annotate type classes for better error messages

- make use of the implicitNotFound annotation to give better compiler errors when there is no available instance of a type class
minor: better implicitNotFound error messages

- improve the language of the error messages: try to avoid mentioning ‘injectivity’, and make suggestions to the user to help correct any errors
- ditch DatomicBij
Merge pull request #80 from pellucidanalytics/topic/implicitNotFound

Annotate type classes for better error messages