Clarify documentation and rename some variables :)

[odrais-amsicorp]

While reviewing the code, I was confused by the comment documentation in Handler.php. It was calculating the number of write lock tries using _breakAfter and _failAfter values correctly, but the comment stated it was in seconds.

The calculation actually returns the number of write lock tries before trying to break the lock and failing to break the lock, respectively. So I've adjusted the documentation appropriately.

I also renamed some properties so it's clearer what they are. And created a utility function to return the number of write lock tries per second.

The PR is here: #60 .

Not necessarily a bug fix, but I believe it's a quality of life fix.