* docstring_parser for extracting argument description.
* determine type using annotations instead of docstring.
* deprecation of --bindto argument; Picatrix magic expect `line`
  argument to be in a following format:

  `{bind_variable} -- {magic_arguments}`

  e.g. `%example var -- 1 2 3 --a=1` will run an `example` magic with
  positional paramters set to `1`, `2` and `3` and keyword argument `a`
  set to `1`. Results will be saved to `var` variable.