Concatenate matrices by specifying them in an Array

[v0dro]

Something like this:

NMatrix.concat([
  [a_nm, b_nm],
  [c_nm, d_nm]
])

[translunar]

So, like hstack/vstack in Numpy? I'm shocked we don't have this, but I can't find it in the code. It ought to be a pretty easy addition.

[v0dro]

We have hconcat and vconcat but its kind of counter intuitive to concatenate when you think of it that way. The easiest way I've come across is the Matlab notation which I think would reflect in nmatrix via this feature.

[translunar]

We should probably also see about aliasing the concat functions to hstack and vstack.