Check usage from Erlang

[PragTob]

It'd be amazing to be a good BEAM citizen and let other languages, specifically Erlang, also use benchee.

Would be great to check if/how benchee can be used from Erlang/rebar3 as package manager and then write down a sample benchmark for using benchee in Erlang in the README.

Of course, also get rid of all incompatibilities. E.g. I'm not sure but right now it might happen that benchee crasses when there is no Elixir version.

[PragTob]

So usage from Erlang has been checked as much as can be, and it should work when it compiles otherwise it is always a way to go to just use benchee from Elixir land and add erlang as a dependency as Elixir understands both systems that's easier.