more documentation

In this commit, also the semantics for values skipped via the parser
callback has changed. Now, the top-level value is returned as “null”
instead of “discarded”.

doc/Doxyfile

@@ -163,7 +163,7 @@ CHM_FILE               =
 HHC_LOCATION           =
 GENERATE_CHI           = NO
 CHM_INDEX_ENCODING     =
-BINARY_TOC             = YES
+BINARY_TOC             = NO
 TOC_EXPAND             = NO
 GENERATE_QHP           = NO
 QCH_FILE               =
@@ -176,7 +176,7 @@ QHG_LOCATION           =
 GENERATE_ECLIPSEHELP   = NO
 ECLIPSE_DOC_ID         = org.doxygen.Project
 DISABLE_INDEX          = NO
-GENERATE_TREEVIEW      = YES
+GENERATE_TREEVIEW      = NO
 ENUM_VALUES_PER_LINE   = 4
 TREEVIEW_WIDTH         = 250
 EXT_LINKS_IN_WINDOW    = NO