Block-diagonal matrix generation

[agisga]

Generate a NMatrix with user-specified square matrices as blocks along its diagonal.
(I wrote such a method for my GSoC project to use for the generation of random effects covariance matrices.)

Example:

a = NMatrix.new([2,2],[1,2,3,4])
b = NMatrix.new([1,1],[123],dtype: :int32)
c = NMatrix.new([3,3],[1,2,3,1,2,3,1,2,3], dtype: :float64)
m = NMatrix.block_diagonal(a,b,c,dtype: :int64, stype: :yale)
    #      => 
    #      [
    #        [1, 2,   0, 0, 0, 0]
    #        [3, 4,   0, 0, 0, 0]
    #        [0, 0, 123, 0, 0, 0]
    #        [0, 0,   0, 1, 2, 3]
    #        [0, 0,   0, 1, 2, 3]
    #        [0, 0,   0, 1, 2, 3]
    #      ]

[agarie]

Fix the spaces in this comment, i.e.:

a = NMatrix.new([2, 2], [1, 2, 3, 4])
b = NMatrix.new([1, 1], [123], dtype: :int32)
c = NMatrix.new([3, 3], [1, 2, 3, 1, 2, 3, 1, 2, 3], dtype: :float64)
m = NMatrix.block_diagonal(a, b, c, dtype: :int64, stype: :yale)

[translunar]

After you fix the line notes, could you please rebase into a single commit?

[agisga]

Additionally to what we have discussed, I have added the possibility to specify the contents of the matrix with single numbers. For example:

NMatrix.block_diag(1, 2.0, 3, [[4,5], [6,7]], dtype: :byte)
# => 
# [ [1, 0, 0, 0, 0]
#   [0, 2, 0, 0, 0]
#   [0, 0, 3, 0, 0]
#   [0, 0, 0, 4, 5]
#   [0, 0, 0, 6, 7] ]