Addi range interface methods to Axis (#176)

Author: Tokazama

src/core.jl

@@ -89,6 +89,10 @@ Base.IteratorEltype(::Type{<:Axis}) = Base.HasEltype()
 Base.iterate(::Type{T}) where {T<:Axis} = (T, nothing)
 Base.iterate(::Type{T}, ::Any) where {T<:Axis} = nothing
 
+Base.first(A::Axis) = first(A.val)
+Base.last(A::Axis) = last(A.val)
+Base.step(A::Axis{name,<:AbstractRange}) where {name} = step(A.val)
+
 """
 An AxisArray is an AbstractArray that wraps another AbstractArray and
 adds axis names and values to each array dimension. AxisArrays can be indexed

test/core.jl

@@ -197,6 +197,9 @@ T = A[AxisArrays.Axis{:x}]
 @test length(Axis{:col}(-1:2)) === 4
 @test AxisArrays.axisname(Axis{:foo}(1:2)) == :foo
 @test AxisArrays.axisname(Axis{:foo})      == :foo
+@test first(Axis{:row}(1:3)) == 1
+@test step(Axis{:row}(1:3)) == 1
+@test last(Axis{:row}(1:3)) == 3
 
 # Test Timetype axis construction
 dt, vals = DateTime(2010, 1, 2, 3, 40), randn(5,2)