Added a method rowAdd(...) to Matrix

[christianbender]

Issue #64
I added the feature as requested:

Adds a multiple of one row to another inside a matrix.

rowAdd(dest : number, source : number, scalar : number = 1.0 ) : Matrix

Inclusive tests

[mateogianolio]

Thanks, will have a look at it this weekend.

[christianbender]

@mateogianolio Super, Thanks.

[mateogianolio]

Some notes:

• Don't create a new array unless you really have to (and if you do, use typed arrays). Array instantiation is expensive, especially when using push() (needs to reallocate memory every time it's called).
• You have two for-loops that loop through the same memory space. They should be combined into one.

See this benchmark: https://jsbench.me/1bjssxmc69/1

[christianbender]

@mateogianolio

• I changed the method rowAdd(...) as requested and made it more effiecient.
• In addition I removed the runtime type checks and changed the test-suite accordingly. Removed the exception-test

[christianbender]

@mateogianolio Done. I added the preconditions again

[codeclimate]

Code Climate has analyzed commit d3faae3 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (80% is the threshold).

This pull request will bring the total coverage in the repository to 90.6% (-3.2% change).

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