Revert "Temporarily remove pat_param."

This reverts commit 629e7df.

Author: ehuss

src/macros-by-example.md

@@ -28,7 +28,7 @@
 >
 > _MacroFragSpec_ :\
 >       `block` | `expr` | `ident` | `item` | `lifetime` | `literal`\
->    | `meta` | `pat` | `path` | `stmt` | `tt` | `ty` | `vis`
+>    | `meta` | `pat` | `pat_param`  | `path` | `stmt` | `tt` | `ty` | `vis`
 >
 > _MacroRepSep_ :\
 > &nbsp;&nbsp; [_Token_]<sub>_except delimiters and repetition operators_</sub>
@@ -122,7 +122,8 @@ fragment specifiers are:
   * `block`: a [_BlockExpression_]
   * `stmt`: a [_Statement_] without the trailing semicolon (except for item
     statements that require semicolons)
-  * `pat`: a [_PatternNoTopAlt_]
+  * `pat_param`: a [_PatternNoTopAlt_]
+  * `pat`: equivalent to `pat_param`
   * `expr`: an [_Expression_]
   * `ty`: a [_Type_]
   * `ident`: an [IDENTIFIER_OR_KEYWORD]