lattice class now has SDEs for
1.TIM xpolarization
2.TIM zpolarization
3. XY model

This choice is made in preprocc with #define values of 1 or 0
- Added y variables and sign variables to trajectory class.
- Added init_traj_y function to lattice class.
- Added evolve_y function to trajectory class but needs to be defined.
Tested zeta function and it seems to work.
Now I need to code it up properly.

At some point I will have to get rid of individual trajectory
writing. Set up a new branch for that.
I have coded up the correct y variable equations and this works fine
as far as I can tell. It still prints out every single trajectory
which is something I want to eliminate. This is the only downside of
this code.