Software license change: LGPLv2

Dear RIOT developers and users,

after long but conclusive discussions, we reached a consensus on the decision to relicense the code with LGPLv2. As a reminder, the goal of this relicensing is (1) to make it possible to link proprietary applications to the core RIOT, without releasing the application source code, and (2) to get rid of patent-related text that many industry lawyers can’t deal with.

We are thus soon going to start modifying accordingly source file headers, website etc.