fix cucumber feature example
add some new grammar pieces

:predcall
  => Person(x), Friend(x,y), True()
:connective_clause
  => Person(x) & Friend(x,y)
:formula
  => :connective_clause OR :predcall

NOTE: Need specs to thoroughly test these
first try at unary clauses, e.g. ~Person(GODZILLA)

NOTE: The following case is broken :(

Person(JANE) & ~Person(KINGKONG)