Prepare for 0.4.0 release

Author: LVala

README.md

@@ -26,7 +26,7 @@ Add `ex_rtp` to dependencies in `mix.exs`:
 ```elixir
 def deps do
   [
-    {:ex_rtp, "~> 0.3.0"}
+    {:ex_rtp, "~> 0.4.0"}
   ]
 end
 ```

mix.exs

@@ -1,7 +1,7 @@
 defmodule ExRTP.MixProject do
   use Mix.Project
 
-  @version "0.3.0"
+  @version "0.4.0"
   @source_url "https://github.com/elixir-webrtc/ex_rtp"
 
   def project do
@@ -10,7 +10,7 @@ defmodule ExRTP.MixProject do
       version: @version,
       elixir: "~> 1.15",
       start_permanent: Mix.env() == :prod,
-      description: "Implementation of RTP protocol",
+      description: "Implementation of the RTP protocol",
       package: package(),
       deps: deps(),