Added engine oscillations

Engine coupling strength now oscillates.
Resolves #13
Racer Properties

Added lots of properties to racers that can be set:
  - Flaps
  - Coupling beams (visuals)
  - Coupling physics
  - Rope length
  - Thrust

Fixes #25.
Moved racer definitions

Moved racer definitions out of PodGameManager.cpp to a new racers.h.
Fixed improper header
Added Races

You can now create races.
Races contain a list of checkpoints and racers.
They keep track of racers' current checkpoint and lap.
Improve Races

Added comments and cleaned up code for races.
Implemented simple AI

Created a simple AI. It controls the thruster ratio to aim toward the
next checkpoint. It also includes some predictive turning when close to
the checkpoint.

Added methods to racer for getting position and direction.
Fixed some improperly written constructors and super()'s.

Closes #10.
Tunable AI difficulty
Improved AI

AI now uses flaps.
Also included a more interesting course.
Sebulba racer is tweaked to be more balanced.
Merge branch '10_AI' into 8_include_lib

Updating latest work to use the new folder structure that includes
angel.