Update rustler_precompiled to v0.4.0 (#64)

Also add Rustler as an optional dependency.

mix.exs

@@ -24,7 +24,8 @@ defmodule Html5ever.Mixfile do
 
   defp deps do
     [
-      {:rustler_precompiled, "~> 0.2"},
+      {:rustler_precompiled, "~> 0.4"},
+      {:rustler, ">= 0.0.0", optional: true},
       {:ex_doc, ">= 0.0.0", only: :dev}
     ]
   end

mix.lock

@@ -1,5 +1,5 @@
 %{
-  "castore": {:hex, :castore, "0.1.16", "2675f717adc700475345c5512c381ef9273eb5df26bdd3f8c13e2636cf4cc175", [:mix], [], "hexpm", "28ed2c43d83b5c25d35c51bc0abf229ac51359c170cba76171a462ced2e4b651"},
+  "castore": {:hex, :castore, "0.1.17", "ba672681de4e51ed8ec1f74ed624d104c0db72742ea1a5e74edbc770c815182f", [:mix], [], "hexpm", "d9844227ed52d26e7519224525cb6868650c272d4a3d327ce3ca5570c12163f9"},
   "earmark_parser": {:hex, :earmark_parser, "1.4.25", "2024618731c55ebfcc5439d756852ec4e85978a39d0d58593763924d9a15916f", [:mix], [], "hexpm", "56749c5e1c59447f7b7a23ddb235e4b3defe276afc220a6227237f3efe83f51e"},
   "ex_doc": {:hex, :ex_doc, "0.28.4", "001a0ea6beac2f810f1abc3dbf4b123e9593eaa5f00dd13ded024eae7c523298", [:mix], [{:earmark_parser, "~> 1.4.19", [hex: :earmark_parser, repo: "hexpm", optional: false]}, {:makeup_elixir, "~> 0.14", [hex: :makeup_elixir, repo: "hexpm", optional: false]}, {:makeup_erlang, "~> 0.1", [hex: :makeup_erlang, repo: "hexpm", optional: false]}], "hexpm", "bf85d003dd34911d89c8ddb8bda1a958af3471a274a4c2150a9c01c78ac3f8ed"},
   "jason": {:hex, :jason, "1.3.0", "fa6b82a934feb176263ad2df0dbd91bf633d4a46ebfdffea0c8ae82953714946", [:mix], [{:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "53fc1f51255390e0ec7e50f9cb41e751c260d065dcba2bf0d08dc51a4002c2ac"},
@@ -8,6 +8,6 @@
   "makeup_erlang": {:hex, :makeup_erlang, "0.1.1", "3fcb7f09eb9d98dc4d208f49cc955a34218fc41ff6b84df7c75b3e6e533cc65f", [:mix], [{:makeup, "~> 1.0", [hex: :makeup, repo: "hexpm", optional: false]}], "hexpm", "174d0809e98a4ef0b3309256cbf97101c6ec01c4ab0b23e926a9e17df2077cbb"},
   "nimble_parsec": {:hex, :nimble_parsec, "1.2.3", "244836e6e3f1200c7f30cb56733fd808744eca61fd182f731eac4af635cc6d0b", [:mix], [], "hexpm", "c8d789e39b9131acf7b99291e93dae60ab48ef14a7ee9d58c6964f59efb570b0"},
   "rustler": {:hex, :rustler, "0.25.0", "32526b51af7e58a740f61941bf923486ce6415a91c3934cc16c281aa201a2240", [:mix], [{:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}, {:toml, "~> 0.6", [hex: :toml, repo: "hexpm", optional: false]}], "hexpm", "6b43a11a37fe79c6234d88c4102ab5dfede7a6a764dc5c7b539956cfa02f3cf4"},
-  "rustler_precompiled": {:hex, :rustler_precompiled, "0.3.0", "47517912d12ccd9e5e950e2ae11c67842261a811233514a60351c560436ea309", [:mix], [{:castore, "~> 0.1", [hex: :castore, repo: "hexpm", optional: false]}, {:rustler, "~> 0.23", [hex: :rustler, repo: "hexpm", optional: false]}], "hexpm", "836dbaaf5bea2538c30a06f89ac1961b6fbfb1eff2dba71fc30b1eecb4a0546e"},
+  "rustler_precompiled": {:hex, :rustler_precompiled, "0.4.0", "427daa55ffa7f61876a890639e06f98c21c2f00783d0c8f7729e03eddaec8e2f", [:mix], [{:castore, "~> 0.1", [hex: :castore, repo: "hexpm", optional: false]}, {:rustler, "~> 0.23", [hex: :rustler, repo: "hexpm", optional: true]}], "hexpm", "baa595201e82910bad9d6163e98f2df7bf9fe83861553fda43cc82e744a49d76"},
   "toml": {:hex, :toml, "0.6.2", "38f445df384a17e5d382befe30e3489112a48d3ba4c459e543f748c2f25dd4d1", [:mix], [], "hexpm", "d013e45126d74c0c26a38d31f5e8e9b83ea19fc752470feb9a86071ca5a672fa"},
 }