Adds y in DynamicalSystem (will be remove from SystemState after).
Change name of dx vector.
Now the access to the vectors is done by the y(index) and dx(index)
functions.
Adds a function to get the y vector size.
Change the integrator to call the new right functions.
Corrects the function declarations.
+ Adds x function to get values of the state.
Completly change de StateStates class definition.
Now this class is an encapsulation of the std::vector class.
Take into account the previous change on SystemState.
Change the Rossler example to match with the new SystemState and
DynamicalSystem definitions.
Change the Network example to match with the previous change of 
SystemState and DynamicalSystem.
Use size_t instead of long.
+ define const the == and != operators
Use local size_type instead of global size_t.
+ Remove useless functions from DynamicalSystem.
Change the "copy" constructor (the copy function MUST be defined).
Changes try example to match with previous modifications in SystemState
and DynamicalSystem.