Added LFE support.

Very excited about this project! LFE on ARM will be fantastic :-)

LFE infos:
 * https://github.com/rvirding/lfe
 * http://lfe.io/
 * http://docs.lfe.io/

If this eventually gets the stamp of approval, do you think we could update the nerves-sdk Github description to the following?

"Platform infrastructure for embedded Erlang/OTP, Elixir and LFE projects"