Step 3 [Handle New Line Delimiter]

* Before adding test for newline delimited created a new test, exactly
the same as testAddTwoDifferentNumbers called
testAddTwoCommaDelimitedNumbers - Tests that passing 2 numbers comma
delimited returns their sum.
* Test passed obviously.
* Debated deleting either add 2 numbers or add 3 numbers but left them
alone for now. I will keep an eye on their value going forward.
* Added test testAddTwoNumbersOnNewLines - Tests that passing 2 numbers
new line delimited returns their sum. that validates "1\n2" returns 3
* refactored code slightly to split on [,\\n] rather than ",".