Simplifying solver interface

[valentinsulzer]

It should be possible to merge

• base_solver, ode_solver and dae_solver into a single base class
• scikits_ode_solver and scikits_dae_solver into a single class

Do you think this would simplify the interface @rtimms ?

[rtimms]

yeah I think that would be good. could we also remove compute_solution and call integrate directly from solve and step? compute_solution saves rewriting the little integrate, get termination reason block of code in both step and solve, but it wouldn't be a massive bit of repetition and would probably be easier to follow for new users. (I think I introduced compute_solution, but I don't like it now haha)

I think the only solver with a drastically different interface is casadi, and we already overwrite some methods there anyway.

[valentinsulzer]

Ok, that sounds good - no worries, compute_solution seemed like a good idea at the time haha