Stochsystem overhaul

[oameye]

Work on #75, #42 and #22

[reykboerner]

I've taken a quick look at this and have three comments:

• CoupledSDEs now has one parameter field p for both functions f and g, but I still think there should be a constructor function that lets you pass individual parameter fields pf and pg as input arguments (because otherwise it will be difficult to combine existing CoupledODEs drift functions with different noise functions).
• We should also import the step! and set_state! functions used in DynamicalSystemsBase and then rewrite the callbacks in e.g. transition in terms of these functions. This seems to be faster than callbacks.
• It makes sense to me that in DynamicalSystemsBase the function should be called CoupledSDEs to match the nomenclature of CoupledODEs, but our package focuses more on noise- and rate-induced transitions, so should we still keep an alias like StochSystem or StochasticSystem?

[oameye]

We should also import the step! and set_state! functions used in DynamicalSystemsBase and then rewrite the callbacks in e.g. transition in terms of these functions. This seems to be faster than callbacks.

The documentation of DynamicalSystems.jl says that recommend using ODEProblem when using callbacks.

[oameye]

We should only merge once the CI, Dowgrade and docs are working. Will take a look tonight :)

[reykboerner]

The transition function throws an error in the tests:

ERROR: cannot assign a value to imported variable CriticalTransitions.trajectory from module Main

Can check later what the issue is. Also, trajectory seems to be a lot slower than simulate. Do you know why @oameye ?

[oameye]

We need to update the docs.

[oameye]

dev, examples and ext have still to be updated

[oameye]

• [x] check how DynamicalSystems of the state and parameters and it similarly
• [ ] Get docs up to date with this branch
• [x] Make extention out of baisins
• [ ] Make helpful constructors for CoupledSDEs
• [ ] Normalise g function in CoupledSDEs and noise strength field

[oameye]

DynamicalSystems allows the parameters to be of the type that the ODEProblem allows.