Made Matrix::from_fn row major, fixes (#172)

[MarkDDR]

Added a test to make sure it is row major as well

I wonder if a better example could be made. The current one is completely symmetrical and doesn't change if row and col get swapped.

[Andlon]

Thanks for this PR! From a brief glance it looks good.

I agree about the example. Do you have anything more suitable in mind?

[Andlon]

(Just mentioning #172 here so that we get a reverse link)