The solution is to use FunctionWrappers.jl which provides a high
interface for C function pointers.

All tests passed.

update_state functions but performance gets worst.
With bench/pkg/abstract_arrays.jl i've highligthed each time a function
is in a collection performance gets worst.

models. It's a better semantic and improve performance as well as
readability of the code. All the tests passes (except the remark in the
last commit).

call of isabsorbing() during the simulation.

Now the package is a bit more efficient than DiffEqJump.jl with the
Catalyst.jl interface which is encouraging, see bench/pkg/catalyst.jl.