Allow vector assignments

Closes #17

See merge request !133

let show_code display/print code

Closes #6

See merge request pycodegen/pystencils!132

Add typeannotations and docstring for KernelWrapper

See merge request !136

- `get_code` will keep the previous behavior of `show_code`
- `get_code_str` will be equivalent to previous `str(show_code(...))`

Fix bug related to ParallelDataHandling

See merge request !130

Fix FiniteDifferenceStencilDerivation.rotate_weights_and_apply

See merge request !128

Print actual block contents in Conditional.{__repr__,__str__}

See merge request !131