Added/removed spaces around logical/arithmetic operator
Reduced multiple empty lines to one empty line
Removed wrong tabs before comments at end of line
Removed too many spaces in assigments
Change-Id: I2bba4e72f9b5f88c53324d7b70e6042f1aad8f6b
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