Link more erlang modules in docs

Author: sabiwara

lib/elixir/lib/json.ex

@@ -356,7 +356,7 @@ defmodule JSON do
     * for `string`: `&Function.identity/1`
     * for `null`: the atom `nil`
 
-  For streaming decoding, see Erlang's `:json` module.
+  For streaming decoding, see Erlang's [`:json`](`:json`) module.
   """
   @spec decode(binary(), term(), keyword()) ::
           {term(), term(), binary()} | {:error, decode_error_reason()}

lib/elixir/lib/kernel.ex

@@ -60,7 +60,7 @@ defmodule Kernel do
 
     * Bitstring - a sequence of bits, created with `<<>>/1`.
       When the number of bits is divisible by 8, they are called binaries and can
-      be manipulated with Erlang's `:binary` module
+      be manipulated with Erlang's [`:binary`](`:binary`) module
     * Reference - a unique value in the runtime system, created with `make_ref/0`
 
   ### Data types
@@ -5722,7 +5722,7 @@ defmodule Kernel do
   >
   >   * If using `defoverridable`, avoid relying on `super` to trigger the default
   >     behaviour, suggesting users to invoke well-defined APIs instead.
-  > 
+  >
   """
   defmacro defoverridable(keywords_or_behaviour) do
     quote do

lib/elixir/lib/string.ex

@@ -172,7 +172,7 @@ defmodule String do
   Standard Annex #29](https://www.unicode.org/reports/tr29/).
 
   For converting a binary to a different encoding and for Unicode
-  normalization mechanisms, see Erlang's `:unicode` module.
+  normalization mechanisms, see Erlang's [`:unicode`](`:unicode`) module.
 
   ## String and binary operations
 

lib/ex_unit/lib/ex_unit.ex

@@ -321,8 +321,8 @@ defmodule ExUnit do
 
     * `:seed` - an integer seed value to randomize the test suite. This seed
       is also mixed with the test module and name to create a new unique seed
-      on every test, which is automatically fed into the `:rand` module. This
-      provides randomness between tests, but predictable and reproducible
+      on every test, which is automatically fed into the [`:rand`](`:rand`) module.
+      This provides randomness between tests, but predictable and reproducible
       results. A `:seed` of `0` will disable randomization and the tests in each
       file will always run in the order that they were defined in;