Add endpoint for room creation

lib/matrix_server_web/api/create_room.ex

@@ -0,0 +1,28 @@
+defmodule MatrixServerWeb.API.CreateRoom do
+  use Ecto.Schema
+
+  import Ecto.Changeset
+
+  alias Ecto.Changeset
+
+  @primary_key false
+  embedded_schema do
+    field :visibility, :string
+    field :room_alias_name, :string
+    field :name, :string
+    field :topic, :string
+    field :invite, {:array, :string}
+    field :room_version, :string
+    # TODO: unimplemented:
+    # creation_content, initial_state, invite_3pid, initial_state, preset,
+    # is_direct, power_level_content_override
+  end
+
+  def changeset(params) do
+    %__MODULE__{}
+    |> cast(params, [:visibility, :room_alias_name, :name, :topic, :invite, :room_version])
+  end
+
+  def get_error(%Changeset{errors: [error | _]}), do: get_error(error)
+  def get_error(_), do: :bad_json
+end