Add anchors in documentation (#4428)

lib/ecto/changeset.ex

@@ -1027,7 +1027,8 @@ defmodule Ecto.Changeset do
 
     * If there is an associated child with an ID and its ID is not given
       as parameter, the `:on_replace` callback for that association will
-      be invoked (see the "On replace" section on the module documentation)
+      be invoked (see the ["On replace" section](#module-the-on_replace-option)
+      on the module documentation)
 
   If two or more addresses have the same IDs, Ecto will consider that an
   error and add an error to the changeset saying that there are duplicate

lib/ecto/query.ex

@@ -870,7 +870,8 @@ defmodule Ecto.Query do
       )
 
   If you need to refer to a parent binding which is not known when writing the subquery,
-  you can use `parent_as` as shown in the examples under "Named bindings" in this module doc.
+  you can use `parent_as` as shown in the examples under ["Named bindings"](#module-named-bindings)
+  in this module doc.
 
   You can also use subquery directly in `select` and `select_merge`:
 
@@ -2885,7 +2886,8 @@ defmodule Ecto.Query do
   @doc """
   Returns `true` if the query has a binding with the given name, otherwise `false`.
 
-  For more information on named bindings see "Named bindings" in this module doc.
+  For more information on named bindings see ["Named bindings"](#module-named-bindings)
+  in this module doc.
   """
   def has_named_binding?(%Ecto.Query{aliases: aliases}, key) do
     Map.has_key?(aliases, key)
@@ -2923,7 +2925,8 @@ defmodule Ecto.Query do
         join(query, :left, [p], a in assoc(p, ^binding), as: ^binding)
       end)
 
-  For more information on named bindings see "Named bindings" in this module doc or `has_named_binding?/2`.
+  For more information on named bindings see ["Named bindings"](#module-named-bindings)
+  in this module doc or `has_named_binding?/2`.
   """
   def with_named_binding(%Ecto.Query{} = query, key, fun) do
     if has_named_binding?(query, key) do

lib/ecto/schema.ex

@@ -822,7 +822,8 @@ defmodule Ecto.Schema do
       association, defaults to the primary key on the schema
 
     * `:through` - Allow this association to be defined in terms of existing
-      associations. Read the section on `:through` associations for more info
+      associations. Read the [section on `:through` associations](#has_many/3-has_many-has_one-through)
+      for more info
 
     * `:on_delete` - The action taken on associations when parent record
       is deleted. May be `:nothing` (default), `:nilify_all` and `:delete_all`.