Continuous to discrete time

[JulienCalbert]

Some solvers work with discrete-time systems, others with continuous-time systems.
We should make a function that converts a continuous-time system into a discrete-time system automatically.

[adrienbanse]

@JulienCalbert Isn't it the purpose of any derivation scheme such as Runge Kutta or explicit Euler?

[blegat]

Runge Kutta and Euler only give you an approximation. Here, you need a guaranteed outer bound (as provided by #302).