Replace Head, Tail, Last, Init by HCons and HSnoc
#138 Propose new syntax
Rename HCons to Cons1 and HSnoc to Snoc1
Merge pull request #134 from julien-truffaut/hcons

Replace Head, Tail, Last, Init by Cons1 and Snoc1
Merge pull request #146 from julien-truffaut/syntax

#138 Propose new syntax
Fix #121 by reducing Tree generation (thanks to @etorreborre)
Merge branch 'master' into nonemptylist
Updated to use cons1 and snoc1.