Add paragraph "Fitting moredimensional datasets" with an example

[antonykamp]

Add paragraph "Fitting moredimensional datasets" with an example from StackOverflow. Solving Issue #143 I corrected the formatting since the last pull request.

[pckroon]

Looks good to me, thanks :)

[tBuLi]

Thanks indeed for helping improve the documentation. It's much appreciated :).

As for the general style of your example, I would prefer it if you first introduce the concept of a multidimensional problem in general, to convey the general idea that we are talking about functions of type :math: z(x_1, \ldots, x_n), such as the temperature distribution on a plane :math:T(x, y) as you had originally.

Then you can move into your polynomial example, introducing :math: z(x, y) = ..., and giving the code example of how to fit to this.

[antonykamp]

What else?

[antonykamp]

Sometimes I don't get the error of Travis CI...can smb help me with this topic pls :D

[tBuLi]

Try building the docs localy first with the same command we use on travis: sphinx-build -nW -b html docs docs_build

That should give you some useful error messages. Usually it is mistakes with indentation and things like that.