Make StarWarsArrays AbstractArray interface compliant

[mkitti]

axes(A) should "Return a tuple of AbstractUnitRange{<:Integer}
of valid indices. The axes should be their own axes, that is
axes.(axes(A),1) == axes(A) should be satisfied."

Instead create a StarWarsArrays.axes and StarWarsArrays.eachindex

[mkitti]

Demonstration

julia> using StarWarsArrays
Precompiling StarWarsArrays
  1 dependency successfully precompiled in 2 seconds

julia> a = StarWarsArray(1:9)
9-element view(::UnitRange{Int64}, [4, 5, 6, 1, 2, 3, 7, 8, 9]) with eltype Int64:
 4
 5
 6
 1
 2
 3
 7
 8
 9

julia> a[1]
4

julia> a[2]
5

julia> a[3]
6

julia> a[4]
1

julia> axes(a)
(Base.OneTo(9),)

julia> StarWarsArrays.axes(a)
([4, 5, 6, 1, 2, 3, 7, 8, 9],)