SiteDiff::log() accepts foreground color now
cleanup: retire SiteDiff::diff_path
default to empty string if no paths are provided

note: this is necessary for being able to diff individual files
make queries in paths work again

note: For SiteDiff 'path' contains path, query, and fragment.
Therfore UriWrapper.path should not be treated as interchangeable
with URI::HTTP.path.
don't die if top level indentation is zero
create diff files in nested directories (a la wget)