From phpcs Change-Id: I919c8af46a722cd1c14bb8c134400e2ec51160d1
Comment some out also Add some bits of documentation
Trimming trailing whitespace also Doing in 3 commits, so hopefully reviewable in CR...
Diff.php -> WikiDiff3.php, more descriptive DifferenceEngine.php -> WikiDiff.php, for consistency with the above and to make way for the file below DifferenceInterface.php -> DifferenceEngine.php, since it contains the DifferenceEngine class