new tutorial on interactive use

Hi,

I have just finished the first draft of a tutorial on interactive use. You can get it at our new repository [1].

<get the updates> cd doc make html <view _build/html/index.html>

It's called Interactive Example: Linear Elasticity.

Unfortunately I can not upload the new generated docs to our site right now, but it should appear soon at [2].

Awaiting feedback, r.

[1] http://github.com/sfepy/sfepy [2] http://docs.sfepy.org/doc-devel