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)


Another location where relative tolerances are in order.