minor symfony#16210 [Yaml] marked some classes as being internal (fabpot)

This PR was merged into the 2.8 branch.

Discussion
----------

[Yaml] marked some classes as being internal

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Adds `@internal` on some YAML classes.

Commits
-------

29e7893 [Yaml] marked some classes as being internal

Author: fabpot

src/Symfony/Component/Yaml/Escaper.php

@@ -16,6 +16,8 @@
  * YAML strings.
  *
  * @author Matthew Lewinski <[email protected]>
+ *
+ * @internal
  */
 class Escaper
 {

src/Symfony/Component/Yaml/Inline.php

@@ -204,6 +204,8 @@ private static function dumpArray($value, $exceptionOnInvalidType, $objectSuppor
      * @return string A YAML string
      *
      * @throws ParseException When malformed inline YAML string is parsed
+     *
+     * @internal
      */
     public static function parseScalar($scalar, $delimiters = null, $stringDelimiters = array('"', "'"), &$i = 0, $evaluate = true, $references = array())
     {

src/Symfony/Component/Yaml/Unescaper.php

@@ -16,6 +16,8 @@
  * YAML strings.
  *
  * @author Matthew Lewinski <[email protected]>
+ *
+ * @internal
  */
 class Unescaper
 {