mdbx: backport - Doxygen fixes. Use DISTRIBUTE_GROUP_DOC.

- DISTRIBUTE_GROUP_DOC makes doxygen give several fields the
  same doc: mn_hi + mn_lo in MDB_node.
- Don't hide a doxygen #name inside double quotes.

Change-Id: I173ff54a78349344d38e175cf9de741efab29e82

Doxyfile

@@ -253,7 +253,7 @@ IDL_PROPERTY_SUPPORT   = YES
 # member in the group (if any) for the other members of the group. By default
 # all members of a group must be documented explicitly.
 
-DISTRIBUTE_GROUP_DOC   = NO
+DISTRIBUTE_GROUP_DOC   = YES
 
 # Set the SUBGROUPING tag to YES (the default) to allow class member groups of
 # the same type (for instance a group of public functions) to be put as a

mdb.c

@@ -614,19 +614,21 @@ typedef struct MDB_page {
 	/** Header for a single key/data pair within a page.
 	 * Used in pages of type #P_BRANCH and #P_LEAF without #P_LEAF2.
 	 * We guarantee 2-byte alignment for 'MDB_node's.
+	 *
+	 * #mn_lo and #mn_hi are used for data size on leaf nodes, and for child
+	 * pgno on branch nodes.  On 64 bit platforms, #mn_flags is also used
+	 * for pgno.  (Branch nodes have no flags).  Lo and hi are in host byte
+	 * order in case some accesses can be optimized to 32-bit word access.
 	 */
 typedef struct MDB_node {
-	/** lo and hi are used for data size on leaf nodes and for
-	 * child pgno on branch nodes. On 64 bit platforms, flags
-	 * is also used for pgno. (Branch nodes have no flags).
-	 * They are in host byte order in case that lets some
-	 * accesses be optimized into a 32-bit word access.
-	 */
+	/** part of data size or pgno
+	 *	@{ */
 #if BYTE_ORDER == LITTLE_ENDIAN
-	unsigned short	mn_lo, mn_hi;	/**< part of data size or pgno */
+	unsigned short	mn_lo, mn_hi;
 #else
 	unsigned short	mn_hi, mn_lo;
 #endif
+	/** @} */
 /** @defgroup mdb_node Node Flags
  *	@ingroup internal
  *	Flags for node headers.