Two more matrixes added with sum test

[JaroslawWiosna]

@michal915 please, have a look at this simple test added by @Przemes . He made pull request to my repo, and I am making this pull request to your master.

• First of all, I wanted to check how double pull request look like,
• Secondly, I wanted @Przemes to know what our project is about, and by making this pull request @Przemes would be familiar with merging procedure. Who knows, perhaps he will join us in the near future in developing or testing or both.
• Eventually, 3 contributors makes MatrixLibs more prestigeous than only two...

So, please merge it as asap as possible. (Travis' build passed)

[michalkielan]

Looks cool, do something useful, after this merged