Add ∅ (empty set) as synonym for Set{Any}({})

Author: jiahao

base/exports.jl

@@ -108,6 +108,7 @@ export
     WeakRef,
     Woodbury,
     Zip,
+    ∅,
 
 # Ccall types
     Cchar,

base/set.jl

@@ -5,6 +5,7 @@ type Set{T}
     Set(itr) = union!(new(Dict{T,Nothing}()), itr)
 end
 Set() = Set{Any}()
+∅ = Set()
 Set(itr) = Set{eltype(itr)}(itr)
 
 show(io::IO, s::Set) = (show(io, typeof(s)); show_comma_array(io, s,"({","})"))