Fix various Doxygen warnings in Haiku book.

- Return tags for methods that don't return anything
- ingroup without matching defgroup
- confusion between ref, a, and link tags (they are not the same)
- missed API changes (BObjectList templated owning, new url
  encode/decode API)
- duplicate defgroup definitions

Change-Id: I94a31b04a10a62e71659522c5ed77098728c0843
Reviewed-on: https://review.haiku-os.org/c/haiku/+/9689
Tested-by: Commit checker robot <[email protected]>
Reviewed-by: waddlesplash <[email protected]>

docs/user/support/BufferedDataIO.dox

@@ -42,9 +42,6 @@
 	\param ownsStream Undocumented
 	\param partialReads Undocumented
 
-	\return Undocumented
-	\retval <value> Undocumented
-
 	\since Haiku R1
 */
 
@@ -53,9 +50,6 @@
 	\fn virtual virtual BBufferedDataIO::~BBufferedDataIO()
 	\brief Undocumented public method
 
-	\return Undocumented
-	\retval <value> Undocumented
-
 	\since Haiku R1
 */