`Parcels` Module

[navidcy]

It'll be fun to write a Parcels module that just advects parcels (or rubber ducks) give a flow field.

[jbisits]

Would the idea behind this module be that the user specifies a flow field $(u(x, y, t), v(x, y, t))$ and an initial position
$(x_{0}, y_{0})$ for the parcel (or rubber duck) then the position of the parcel,
$(x(t), y(t))$ in physical space, evolves according to

$$ \begin{aligned} \frac{d x}{d t} &= u(x(t), y(t), t) \\ \frac{d y}{d t} &= v(x(t), y(t), t) \end{aligned} $$

in two dimensions (though could be generalised for one and three dimensions and many parcels as well)? So it would be a matter of setting up a Parcels.Problem in the module that solved the above in Fourier space?