Doc comment maintenance

Fixed doc comments issues:

* Fixed mistyped param doc comments (`/**<` is OK, `/** <` is not).

* Put special characters (e.g., pipe, backslash, etc.) in quotes, as they can
  confuse doxygen and it will print lots of various warnings. For the sake of
  completeness and consistent style, also quote some special characters in
  re-bytecode.h

* Added missing `@{`s, removed extra `@}`s.

* Turned `/*` comments to `/**<` doc comments.

Ensured same style for doc groups everywhere:

* Where `\addtogroup`, `@{`, and `@}` doxygen commands are used, the order to be
  followed is: license, `#ifndef` guards (in headers), includes, `\addtogroup`
  and `@{`, main code content, `@}`, `#endif` guards (in headers).

* Multiple `\addtogroup`s or multiple `@}`s should be in the same doc comment.

* First `\addtogroup` should be on the very first line of a doc comment, i.e.,
  `/** \addtogroup`.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

jerry-core/ecma/base/ecma-gc.h

@@ -1,4 +1,4 @@
-/* Copyright 2014-2015 Samsung Electronics Co., Ltd.
+/* Copyright 2014-2016 Samsung Electronics Co., Ltd.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -13,6 +13,12 @@
  * limitations under the License.
  */
 
+#ifndef ECMA_GC_H
+#define ECMA_GC_H
+
+#include "ecma-globals.h"
+#include "mem-allocator.h"
+
 /** \addtogroup ecma ECMA
  * @{
  *
@@ -20,12 +26,6 @@
  * @{
  */
 
-#ifndef ECMA_GC_H
-#define ECMA_GC_H
-
-#include "ecma-globals.h"
-#include "mem-allocator.h"
-
 extern void ecma_gc_init (void);
 extern void ecma_init_gc_info (ecma_object_t *);
 extern void ecma_ref_object (ecma_object_t *);
@@ -33,9 +33,9 @@ extern void ecma_deref_object (ecma_object_t *);
 extern void ecma_gc_run (void);
 extern void ecma_try_to_give_back_some_memory (mem_try_give_memory_back_severity_t);
 
-#endif /* !ECMA_GC_H */
-
 /**
  * @}
  * @}
  */
+
+#endif /* !ECMA_GC_H */