Make the result of a binary rule compatible with the in/out attributes of the pair of operators
implement [unary](/pyoperators/2000/doc-operators/#unary_rules rules instead of the less flexible ‘associated_operators’ mechanism
add shape_input, shape_output, inplace and inplace_reductions to operator’s [flags](/pyoperators/2000/doc-operators/#operator_flags
DirectOperatorFactory and ReverseOperatorFactory
ZeroOperator to handle inplace reductions
API changes: block operators must be instanciated with a axisin(out) or new_axisin(out) keyword, the default call without any keyword is reserved for future free partitioning