Add JuAFEM usage example

[TeroFrondelius]

As discussed earlier with @IvanYashchuk. We should add the demo, how to use Materials.jl together with JuaFEM.

[IvanYashchuk]

Here are the files https://gist.github.com/IvanYashchuk/1849515421cb9a229c1f672d1c93f148
nbviewer1 nbviewer2
I won't have time to submit PR and make same Literate.jl example in near future as I'm on holidays.