Added two options to correct file paths if they differ in the merged files

[LexxFedoroff]

Closes #24

# ./bin/phpunit-merger help coverage
Description:
  Merges multiple PHPUnit coverage php files into one

Usage:
  coverage [options] [--] <directory> [<file>]

Arguments:
  directory                            The directory containing PHPUnit coverage php files
  file                                 The file where to write the merged result. Default: Standard output

Options:
...
      --projectRoot=PROJECTROOT        The path to the project source code
      --fixRoot[=FIXROOT]              The root path that will be replaced with the project root path (multiple values allowed)