Stochastic models

[seabbs]

Make stochastic models have parity with current ODE implementations

Jobs

• [ ] Implement a solving function for stochastic models
• [ ] Implement all models as stochastic
• [ ] Testing for all stochastic models
• [ ] Support for multiple model runs in all functions

[seabbs]

Stochastic models have less of a standard R implementation. See epirecipes for some standards.

Want to avoid heavy fitting packages, cryptic model structures etc.