BUG: integrate: Fix some bugs and documentation errors in the ode solvers.

This pull request continues https://github.com/scipy/scipy/pull/3206.  Specifically, it fixes the handling of banded Jacobians in the `vode` solver and in the `complex_ode` class, and fixes some documentation mistakes.
It would probably be reasonably simple to check here if `jac` is pre-padded by the user routine or not, to maintain backward compatibility.