:arrow_up: update Doxyfile for doxygen 1.9.0

doc/Doxyfile

diff --git a/doc/Doxyfile b/doc/Doxyfile
index 9884f95..45ca882 100644
--- a/doc/Doxyfile
+++ b/doc/Doxyfile
@@ -1,4 +1,4 @@
-# Doxyfile 1.8.19
+# Doxyfile 1.9.0
 
 #---------------------------------------------------------------------------
 # Project related configuration options
@@ -26,6 +26,7 @@
 JAVADOC_BANNER         = NO
 QT_AUTOBRIEF           = NO
 MULTILINE_CPP_IS_BRIEF = NO
+PYTHON_DOCSTRING       = YES
 INHERIT_DOCS           = YES
 SEPARATE_MEMBER_PAGES  = YES
 TAB_SIZE               = 4
@@ -54,6 +55,7 @@
 INLINE_SIMPLE_STRUCTS  = NO
 TYPEDEF_HIDES_STRUCT   = NO
 LOOKUP_CACHE_SIZE      = 0
+NUM_PROC_THREADS       = 1
 #---------------------------------------------------------------------------
 # Build related configuration options
 #---------------------------------------------------------------------------
@@ -65,6 +67,7 @@
 EXTRACT_LOCAL_CLASSES  = YES
 EXTRACT_LOCAL_METHODS  = YES
 EXTRACT_ANON_NSPACES   = YES
+RESOLVE_UNNAMED_PARAMS = YES
 HIDE_UNDOC_MEMBERS     = NO
 HIDE_UNDOC_CLASSES     = NO
 HIDE_FRIEND_COMPOUNDS  = NO
@@ -143,7 +146,6 @@
 # Configuration options related to the alphabetical class index
 #---------------------------------------------------------------------------
 ALPHABETICAL_INDEX     = YES
-COLS_IN_ALPHA_INDEX    = 5
 IGNORE_PREFIX          =
 #---------------------------------------------------------------------------
 # Configuration options related to the HTML output
@@ -307,6 +309,8 @@
 GROUP_GRAPHS           = YES
 UML_LOOK               = YES
 UML_LIMIT_NUM_FIELDS   = 10
+DOT_UML_DETAILS        = NO
+DOT_WRAP_THRESHOLD     = 17
 TEMPLATE_RELATIONS     = NO
 INCLUDE_GRAPH          = NO
 INCLUDED_BY_GRAPH      = NO