Refactor Contractor so that the call is a standard function call (#48)

* Refactor flatAST with methods

* FlattenedAST -> FlatAST

* forward_backward replaces forward_pass and backward_pass

* Working NewContractor with action via function call

* Make contractors in separators use new syntax (accepting IntervalBox. This seems to break pave -- when empty?

* Finish rewrite to use forward_backward. Contractor call is messy.

* Clean up functions

* Clean up contractor code

* Clean up separator code

* Add  for contractor call

* Make contractors return IntervalBox'es and deal with fallout

* Correct sqr_rev

Author: dpsanders

src/IntervalConstraintProgramming.jl

@@ -32,5 +32,9 @@ include("setinversion.jl")
 include("volume.jl")
 include("functions.jl")
 
+import Base.∪
+import ValidatedNumerics: IntervalBox
+∪{N,T}(X::IntervalBox{N,T}, Y::IntervalBox{N,T}) =
+    IntervalBox( [(x ∪ y) for (x,y) in zip(X, Y)]... )
 
 end # module