Vode_ODEsystem: add support for other integrators from scipy.integrate.ode

[z2v]

Vode_ODEsystem is based on scipy.integrate.ode, which supports several integrators ("vode", "lsoda", "dorpi5", "dop853"). Suggestion: make it possible to select integrator somehow.

Possible solutions:

• Add option to Vode_ODEsystem for selected integrator (defaulting to "vode" for backward compatibility), rename generator accordingly and deprecate using Vode_ODEsystem.
• Create generators for all integrators (What name to use for "dopri5"? We already have Dopri_ODEsystem!) with common functionality extracted to base class (no copy-paste!).

I vote for the option. It seems to be much easier to fulfill.

[robclewley]

This could be useful, yes. I vote for the option too. It doesn't matter if there's two "versions" of dopri there. The scipy one will be accessible to people without a compiler anyway, even if it will be slower. I'll have to check and see if there's anything changed about the API since I kept my own copy of the ode solver class but a quick glance suggests it should be straightforward.