Also import the license.txt file
Update to Atmel LWM version 1.2.1

This imports (part of) the code from the "Lightweight Mesh Software
Stack v1.2.1" zipfile, as downloaded from the [atmel website][1].

[1]: http://www.atmel.com/tools/lightweight_mesh.aspx
Add a README

This gives a short introduction and clarifies the licensing.