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.
Passing `a` and `exact_sol` via generators makes the test output look like
```
test_banded_ode_solvers.test_banded_ode_solvers(array([[-0.6,  0. ,  0. ,  0. ,  0. ], ... ok
```
so you don't actually get to see what the parameters of the test were, and cannot know which one failed, especially if they run out of order.

This can be avoided by never passing arrays to test generators, and only iterating over test parameters.