Jason is now a common default, remove usage instructions

Author: michalmuskala

README.md

@@ -39,56 +39,18 @@ Full documentation can be found at [https://hexdocs.pm/jason](https://hexdocs.pm
 
 ### Postgrex
 
-You need to define a custom "types" module in an `.ex` file, somewhere in `lib`:
+Versions starting at 0.14.0 use `Jason` by default. For earlier versions, please refer to
+[previous versions of this document](https://github.com/michalmuskala/jason/tree/v1.1.2#postgrex).
 
-```elixir
-Postgrex.Types.define(MyApp.PostgresTypes, [], json: Jason)
-
-## If using with ecto, you also need to pass ecto default extensions:
-
-Postgrex.Types.define(MyApp.PostgresTypes, [] ++ Ecto.Adapters.Postgres.extensions(), json: Jason)
-```
-
-Then you can use the module, by passing it to `Postgrex.start_link`.
 ### Ecto
 
-To replicate fully the current behaviour of `Poison` when used in Ecto applications,
-you need to configure `Jason` to be the default encoder of the `postgrex` library, in `config/config.exs`:
-
-```elixir
-config :postgrex, :json_library, Jason
-```
-
-Additionally, when using PostgreSQL, you need to define a custom types module as described
-above, and configure your repo to use it (in either `config/config.exs` or `config/<env>.exs`):
-
-```elixir
-config :my_app, MyApp.Repo, types: MyApp.PostgresTypes
-```
+Versions starting at 3.0.0 use `Jason` by default. For earlier versions, please refer to
+[previous versions of this document](https://github.com/michalmuskala/jason/tree/v1.1.2#ecto).
 
 ### Plug (and Phoenix)
 
-First, you need to configure `Plug.Parsers` to use `Jason` for parsing JSON. You need to find,
-where you're plugging the `Plug.Parsers` plug (in case of Phoenix, it will be in the
-Endpoint module) and configure it in your endpoint module (`lib/app_web/endpoint.ex`),
-for example:
-
-```elixir
-plug Plug.Parsers,
-  parsers: [:urlencoded, :multipart, :json],
-  pass: ["*/*"],
-  json_decoder: Jason
-```
-
-Additionally, for Phoenix, you need to configure the "encoder" in `config/config.exs`:
-
-```elixir
-config :phoenix, :format_encoders,
-  json: Jason
-```
-
-A custom JSON encoder for Phoenix channels is unfortunately a bit more involved,
-you can find code for a custom serializer and how to use it [in here](https://gist.github.com/michalmuskala/d5fabcd26be2befdfb72b72e0b0f2797).
+Phoenix starting at 1.4.0 uses `Jason` by default. For earlier versions, please refer to
+[previous versions of this document](https://github.com/michalmuskala/jason/tree/v1.1.2#plug-and-phoenix).
 
 ### Absinthe