Function manifold chart

Created a FunctionManifoldChart. If you have two Functions (or two expressions) that describe your push_forward and pull_back methods of ManifoldChart, then this class allows you to construct a Manifold on the fly.

An example with "x^2; y^2; z^2" and "sqrt(x); sqrt(y); sqrt(z)":

![screen shot 2014-08-07 at 14 48 12](https://cloud.githubusercontent.com/assets/2919756/3842086/270b7c78-1e34-11e4-818b-93f174b2c3d0.png)

![screen shot 2014-08-07 at 14 49 04](https://cloud.githubusercontent.com/assets/2919756/3842090/3157c89e-1e34-11e4-9de9-1d483ede5904.png)


The comment doesn't really say what the variable actually means. Maybe something like
  "Indicate whether this class is the owner of the objects pointed to by the previous two member variables.
   This value is set in the constructor of the class. If #true, then the destructor will delete the function
   objects pointed to be the two pointers."