Tests for data with empty lines

[mbtools]

I appreciate the tests included with the repo. I'm porting the solution to another language. My port was not working when the input data had empty lines. I noticed that none of the test cases included empty lines. Might be worth adding some.

For example:

    const a = ['AA', '', 'b', 'c', 'ZZ', '', 'z', '', '', '90', '', 'x'];
    const b = ['AA', '', 'd', 'c', 'ZZ', '', '', 'z', '', '99', '', 'x'];
    const result = Diff3.diffComm(a, b);