Develop v2 ease exponential

Please ignore my previous pull request, it was going to the wrong branch.... Sorry, not an experienced user of github.
https://github.com/cocos2d/cocos2d-iphone/pull/297



*** Description of issue and solution ***

The issue with exponential functions is that they exhibit asymptotes. 
The effects of the asymptotes become visible when performing large changes over a short time.
i.e. rotate 10000 degrees in 2.5 seconds with an exponential ease out, the effect is that as it comes to a stop, it jumps to its final position.

ExponentialEaseOut will asymptote at newT = 1 while ExponentialEaseIn will asymptote at newT = 0, hence the original version hard coded these values for newT.

I have replaced the exponential mathematical routine with a nth order polynomial which resembles an exponential curve for values of 0 <= t <= 1 and an order of 6.
The advantage of using polynomial curves is that they do not asymptote.
I have allowed for odd and even values of polynomial orders as odd values will exhibit an inflection in the curve.

As a feature of this curve, you can now control the acceleration at which it eases in or out by adjusting the polynomial value, polynomial must be greater than 1.



*** Demonstration of theory ***

The attached image shows the following:
Purple curve = Exponential Curve for EaseOut, asymptotes at y = 1
Red curve = 6th order polynomial for EaseOut, y =1 when x = 1
Green curve = Exponential Curve for EaseIn, asymptotes at y = 0
Dark Blue curve = 6th order polynomial for EaseIn, y =0 when x = 0
Brown and light blue curve represent an EaseInOut 6th order polynomial were y = 0 when x = 0 and y = 1 when x = 1.
![CCEasePolynomial](https://f.cloud.github.com/assets/1904325/229034/bdb7d616-8692-11e2-88ca-f3a2f4e652ff.png)



*** Code Details ***

- added an abstract class called CCEaseExponential where it will store polynomial order, inflection attribute and intersect point for InOut action based on the polynomial order
- added property for abstract class to change the order of the polynomial to control acceleration of the ease function
- Modified CCEaseExponentialIn to use polynomial curves of newT = t^n  where n > 1
- Modified CCEaseExponentialOut to use polynomial curves of newT = (t - 1)^n + 1  where n > 1 and is an odd integer, newT = -( (t - 1)^n ) + 1  where n > 1 and is an even integer
- Modified CCEaseExponentialInOut (for 0 <= t < 0.5) to use polynomial curves of newT = (t * intersect)^n  where n > 1,
- Modified CCEaseExponentialInOut (for 0.5 <= t <= 1) to use polynomial curves of newT = ( (t - 1) * intersect)^n + 1  where n > 1 and is an odd integer, newT = -( ( (t - 1) * * intersect ) ^n ) + 1  where n > 1 and is an even integer