Add multiplication for RectDiagonal

[dlfivefifty]

This is inconsistent:

julia> 2Eye(10)
10×10 Diagonal{Float64,Fill{Float64,1,Tuple{Base.OneTo{Int64}}}}:
 2.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅   2.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅   2.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅   2.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅   2.0   ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅   2.0   ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   2.0   ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   2.0   ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   2.0   ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   2.0

julia> 2Eye(10,10)
10×10 Array{Float64,2}:
 2.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0
 0.0  2.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0
 0.0  0.0  2.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0
 0.0  0.0  0.0  2.0  0.0  0.0  0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0  2.0  0.0  0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0  0.0  2.0  0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0  0.0  0.0  2.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0  0.0  0.0  0.0  2.0  0.0  0.0
 0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  2.0  0.0
 0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  2.0

[Wu-Chenyang]

Currently, scalar multiplication of RectDiagonal{<:Number,<:AbstractFill} results in RectDiagonal{<:Number,<:Vector}. For example,

julia> 2Eye(10,10)
2Eye(10,10)
10×10 FillArrays.RectDiagonal{Float64, Vector{Float64}, Tuple{Base.OneTo{Int64}, Base.OneTo{Int64}}}:
 2.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅   2.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅   2.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅   2.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅   2.0   ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅   2.0   ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   2.0   ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   2.0   ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   2.0   ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   2.0

This can be easily fixed by adding the following two methods:

Base.:*(a::FillArrays.RectDiagonal{<:Number, <:FillArrays.AbstractFill}, b::Number) = FillArrays.RectDiagonal(a.diag * b, a.axes)
Base.:*(a::Number, b::FillArrays.RectDiagonal{<:Number, <:FillArrays.AbstractFill}) = FillArrays.RectDiagonal(a * b.diag, b.axes)