Standardize "Examples" heading section levels in docs (#14638)

* Convert "Examples" 3rd level headings to 2nd level when not under a 2nd level

* Convert 1st level "Examples" heading to 2nd level

Author: eksperimental

lib/elixir/lib/calendar/date.ex

@@ -321,7 +321,7 @@ defmodule Date do
   @doc """
   Converts the given date to a string according to its calendar.
 
-  ### Examples
+  ## Examples
 
       iex> Date.to_string(~D[2000-02-28])
       "2000-02-28"
@@ -399,7 +399,7 @@ defmodule Date do
   or other calendars in which the days also start at midnight.
   Attempting to convert dates from other calendars will raise an `ArgumentError`.
 
-  ### Examples
+  ## Examples
 
       iex> Date.to_iso8601(~D[2000-02-28])
       "2000-02-28"

lib/elixir/lib/calendar/datetime.ex

@@ -1046,7 +1046,7 @@ defmodule DateTime do
   its abbreviation, which means information is lost when converting to such
   format.
 
-  ### Examples
+  ## Examples
 
       iex> dt = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "CET",
       ...>                hour: 23, minute: 0, second: 7, microsecond: {0, 0},
@@ -1390,7 +1390,7 @@ defmodule DateTime do
   custom (but relatively common) representation which appends the time
   zone abbreviation and full name to the datetime.
 
-  ### Examples
+  ## Examples
 
       iex> dt = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "CET",
       ...>                hour: 23, minute: 0, second: 7, microsecond: {0, 0},
@@ -1636,7 +1636,7 @@ defmodule DateTime do
   not currently supported in Elixir's standard library but it is available
   by third-party libraries.
 
-  ### Examples
+  ## Examples
 
       iex> dt = DateTime.from_naive!(~N[2018-11-15 10:00:00], "Europe/Copenhagen", FakeTimeZoneDatabase)
       iex> dt |> DateTime.add(3600, :second, FakeTimeZoneDatabase)

lib/elixir/lib/calendar/naive_datetime.ex

@@ -761,7 +761,7 @@ defmodule NaiveDateTime do
   For readability, this function follows the RFC3339 suggestion of removing
   the "T" separator between the date and time components.
 
-  ### Examples
+  ## Examples
 
       iex> NaiveDateTime.to_string(~N[2000-02-28 23:00:13])
       "2000-02-28 23:00:13"
@@ -908,7 +908,7 @@ defmodule NaiveDateTime do
   Only supports converting naive datetimes which are in the ISO calendar,
   attempting to convert naive datetimes from other calendars will raise.
 
-  ### Examples
+  ## Examples
 
       iex> NaiveDateTime.to_iso8601(~N[2000-02-28 23:00:13])
       "2000-02-28T23:00:13"

lib/elixir/lib/calendar/time.ex

@@ -225,7 +225,7 @@ defmodule Time do
   @doc """
   Converts the given `time` to a string.
 
-  ### Examples
+  ## Examples
 
       iex> Time.to_string(~T[23:00:00])
       "23:00:00"
@@ -334,7 +334,7 @@ defmodule Time do
   format, for human readability. It also supports the "basic" format through
   passing the `:basic` option.
 
-  ### Examples
+  ## Examples
 
       iex> Time.to_iso8601(~T[23:00:13])
       "23:00:13"

lib/elixir/lib/kernel.ex

@@ -2815,7 +2815,7 @@ defmodule Kernel do
   This is most commonly used in pipelines, using the `|>/2` operator, allowing you
   to pipe a value to a function outside of its first argument.
 
-  ### Examples
+  ## Examples
 
       iex> 1 |> then(fn x -> x * 2 end)
       2

lib/elixir/lib/list.ex

@@ -915,7 +915,7 @@ defmodule List do
 
   If `prefix` is an empty list, it returns `true`.
 
-  ### Examples
+  ## Examples
 
       iex> List.starts_with?([1, 2, 3], [1, 2])
       true
@@ -945,7 +945,7 @@ defmodule List do
 
   If `suffix` is an empty list, it returns `true`.
 
-  ### Examples
+  ## Examples
 
       iex> List.ends_with?([1, 2, 3], [2, 3])
       true

lib/elixir/lib/version.ex

@@ -442,7 +442,7 @@ defmodule Version do
 
   If `string` is an invalid requirement, a `Version.InvalidRequirementError` is raised.
 
-  # Examples
+  ## Examples
 
       iex> Version.parse_requirement!("== 2.0.1")
       Version.parse_requirement!("== 2.0.1")
@@ -485,7 +485,7 @@ defmodule Version do
   @doc """
   Converts the given version to a string.
 
-  ### Examples
+  ## Examples
 
       iex> Version.to_string(%Version{major: 1, minor: 2, patch: 3})
       "1.2.3"