===
Minor incompatibilty - ``DepsReader.read`` no longer accepts a
``var_name`` parameter.
19: DepsReader.read and DepsReader.try_read now return a
scripts.Dependencies instance, which always has an
``index_url`` attribute whose value will reflect
the value of ``__index_url__`` from the script (if present)
or None otherwise.
19: For standalone scripts, if ``__index_url__`` is indicated,
it will be used to resolve dependencies.