Another LFE Example

In between projects at university, I started working through [these exercises](http://www.erlang.org/course/exercises.html) to reacquaint myself with Erlang/LFE and thought it might be nice to have them included in the examples for LFE. They're nothing spectacular and probably require some adjustments for style alone, but I found the exercises were good for getting in the Erlang groove.

Too trivial ?