fix some code style and add checks to ci

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/eventos/slug.ex

@@ -0,0 +1,16 @@
+defmodule Eventos.Slug do
+  @moduledoc """
+  Common functions for slug generation
+  """
+  def increment_slug(slug) do
+    case List.pop_at(String.split(slug, "-"), -1) do
+      {nil, _} ->
+        slug
+      {suffix, slug_parts} ->
+        case Integer.parse(suffix) do
+          {id, _} -> Enum.join(slug_parts, "-") <> "-" <> Integer.to_string(id + 1)
+          :error -> slug <> "-1"
+        end
+    end
+  end
+end