Compatibility fix for rebar 2.1.0
  rebar_config:get_global/2 changed to get_global/3 with rebar 2.1.0
  add code which checks exports for arity of get_global
Merge pull request #12 from qhool/rebar_2_1_0_fix

Compatibility fix for rebar 2.1.0
Compile Elixir module on pre_compile so they make it to the .app file