#90 Add Cons and Snoc + refactor Prism and Optional constructor
#90 Add Cons Snoc laws
Make methods final
Correct Snoc implementations
#90 Add Emtpy and refactor Cons Snoc laws to Sequence laws
Merge pull request #123 from julien-truffaut/cons

#90 Add Cons, Snoc and Empty + refactor Prism and Optional constructor