Fix elementary Matrix construction bug

[pstaabp]

Fix a bug related to elementary matrices, fix the test and add some additional tests for elementary matrices.

This is to fix #1371

[drgrice1]

There is another problem with this file that seems to be rather prevalent in the POD. It seems that you did this in the previous pull request that changed the POD in this file. These really don't make any sense. Read the Row Swap section. Does that really make sense to you? I mean just look at the first sentence:

To perform a row swap between rows i and j, then E(n,[i, j]).

It looks like the sentence was not supposed to end and the Usage got inject where it shouldn't be. But even if you remove the Usage part and the period in the above statement the resulting sentence is still rather nonsensical.

[pstaabp]

I think you're saying that it's not clear what E(n,[i],k) does? Would this sound better?

To create the matrix that will multiply a row C<i>, by constant C<k>, then C<E(n,[i],k)> 
produces the n by n elementary matrix that performs the row multiplication. 

[drgrice1]

No, that really isn't better.

First, the E method is an object method. It cannot be called as E(n, [i], k). So that should never appear that way in the POD.

Second your grammatical structure is logically incorrect. You should never have "To create .. then". That makes no sense. The logical structure is If .. then .., but even that is probably not what is needed here.

Also, Just changing that sentence is not enough. The whole section needs to be reworked.