Oflibpytorch 2.1.1

oflibpytorch 2.1.1 (Optical Flow Library, pytorch version)

Changelog:

• Flow method 'unpad' introduced: effectively a helper function to undo Flow.pad
• Flow method 'from_transforms' signature extended by a padding argument: convenience when creating
  a padded flow field, automatically adjusting the shape and relevant transform parameters
• Flow method 'select' parameter item can be None, returning self
• Flow method 'get_padding' signature extended by an item argument, used to select an item in the
  batched flow. Returns a simple list of padding values, rather than a list of lists.
• Minor performance improvement in Flow method 'combine'