Adding in timing changes to 'AO_sim' option. Now properly
calculates the time the simulations take.
Added the ability to track the maximum pressure and other attributes
by including a 'Statistics' structure. This information is printed out
after the run of the simulation for decifering when (time step) the
ultrasound reaches the focus, for instance.

Also cleaned up the timing changes a bit. Committing this to be merged
into the 'developement' branch, which then needs to be merged into 'master'
after some more rigourous testing.