builds and tests with mix

[rixmann]

No description provided.

[liveforeverx]

@rixmann - the mix way shouldn't be preferenced way of building dike. erlang applications should be definitely build with rebar, and README should reflect it too.

mix.exs - can exists, as better alternative (as in hello too) for somebody, as we, who use it with elixir projects, but rebar should be preferred way, as it allows elixir and erlang(both) to use. And should be always possible to build without elixir(rebar should maintained). And, at least, the README should reflect rebar build way at first.