BUGFIX: LockStepLink.h did not have include guards.
Render Engine: store dimensions as floats, and make const getters.
Code Style: Constructors with initializer lists indent the lists.

* Also, the colons and commas are at the beginning of each line, not
  the end.
Simulation: Created the Simulation class (a type of display link).

* Now the VisualisationEngine takes a simulation to initialise itself
  with.
* It holds the SimulationEngine (a type of Render Engine) and a
  SimState (a type of Screen, or Render Target).