Deprecate stream variables (#933)

docs/api/variables/streams.md

@@ -10,4 +10,7 @@ template.
 {$foo:bar}
 ```
 
+NB. Support for using streams to call variables is deprecated since Smarty v5.1 and will be removed
+in a future version. 
+
 See also [`Template Resources`](../resources.md)

src/Template.php

@@ -555,6 +555,9 @@ class Template extends TemplateBase {
 	 */
 	public function getStreamVariable($variable)
 	{
+
+		trigger_error("Using stream variables (\`\{\$foo:bar\}\`)is deprecated.", E_USER_DEPRECATED);
+
 		$_result = '';
 		$fp = fopen($variable, 'r+');
 		if ($fp) {