Removed a rebar.config entry that is not required and added some example apps in erlang and elixir

[aramallo]

At the moment Elixir fails on the first compile, but succeds on the second one. To replicate do

rm -rf deps _build priv
mix deps.get
mix compile

That will fail with sth like

** (Mix) Could not compile dependency :cozo, "/Users/foo/.mix/elixir/1-15/rebar3 bare compile --paths /Users/foo/cozo/examples/elixir_app/_build/dev/lib/*/ebin" command failed. Errors may have been logged above. You can recompile this dependency with "mix deps.compile cozo --force", update it with "mix deps.update cozo" or clean it with "mix deps.clean cozo"

Then the following should work

mix compile
iex -S mix