Document additional Matrix Row Operations and add their Columnar counterparts

[Aweptimum]

While working on #459, I noticed that there's a NumericMatrix->rowAddScalar() method that isn't documented and that there is no matching columnAddScalar. Should this be rectified? I couldn't find an issue referencing their implementation.

Edit: Noticed there's also rowSubtract and rowSubtractScalar

[markrogoyski]

Hi @Aweptimum,

Thank you for your interest in improving MathPHP.

When you say not documented, are you referring to the main README on the Github main project page, or in some PHPDoc comments in the code?

Thanks, Mark

[Aweptimum]

Just the main README. The doc blocks are perfectly fleshed out.

[markrogoyski]

Thanks. I've updated the README in the develop branch.

I think it makes sense to add corresponding column methods. If you would like to work on this let me know. Otherwise, I'll put it on my to-do list.

Thanks, Mark

[markrogoyski]

The README has been fixed in the latest version v2.7.0.

[Aweptimum]

Should be easy enough, I could probably do it Monday

Edit: I unfortunately do not have the time today :/