Try to reduce RTD memory usage

docs/Doxyfile_rtd

@@ -2130,7 +2130,7 @@ PERL_PATH              = /usr/bin/perl
 # powerful graphs.
 # The default value is: YES.
 
-CLASS_DIAGRAMS         = YES
+CLASS_DIAGRAMS         = NO
 
 # You can define message sequence charts within doxygen comments using the \msc
 # command. Doxygen will then run the mscgen tool (see:
@@ -2203,7 +2203,7 @@ DOT_FONTPATH           =
 # The default value is: YES.
 # This tag requires that the tag HAVE_DOT is set to YES.
 
-CLASS_GRAPH            = YES
+CLASS_GRAPH            = NO
 
 # If the COLLABORATION_GRAPH tag is set to YES then doxygen will generate a
 # graph for each documented class showing the direct and indirect implementation
@@ -2212,14 +2212,14 @@ CLASS_GRAPH            = YES
 # The default value is: YES.
 # This tag requires that the tag HAVE_DOT is set to YES.
 
-COLLABORATION_GRAPH    = YES
+COLLABORATION_GRAPH    = NO
 
 # If the GROUP_GRAPHS tag is set to YES then doxygen will generate a graph for
 # groups, showing the direct groups dependencies.
 # The default value is: YES.
 # This tag requires that the tag HAVE_DOT is set to YES.
 
-GROUP_GRAPHS           = YES
+GROUP_GRAPHS           = NO
 
 # If the UML_LOOK tag is set to YES, doxygen will generate inheritance and
 # collaboration diagrams in a style similar to the OMG's Unified Modeling
@@ -2257,7 +2257,7 @@ TEMPLATE_RELATIONS     = NO
 # The default value is: YES.
 # This tag requires that the tag HAVE_DOT is set to YES.
 
-INCLUDE_GRAPH          = YES
+INCLUDE_GRAPH          = NO
 
 # If the INCLUDED_BY_GRAPH, ENABLE_PREPROCESSING and SEARCH_INCLUDES tags are
 # set to YES then doxygen will generate a graph for each documented file showing
@@ -2266,7 +2266,7 @@ INCLUDE_GRAPH          = YES
 # The default value is: YES.
 # This tag requires that the tag HAVE_DOT is set to YES.
 
-INCLUDED_BY_GRAPH      = YES
+INCLUDED_BY_GRAPH      = NO
 
 # If the CALL_GRAPH tag is set to YES then doxygen will generate a call
 # dependency graph for every global function or class method.
@@ -2297,7 +2297,7 @@ CALLER_GRAPH           = YES
 # The default value is: YES.
 # This tag requires that the tag HAVE_DOT is set to YES.
 
-GRAPHICAL_HIERARCHY    = YES
+GRAPHICAL_HIERARCHY    = NO
 
 # If the DIRECTORY_GRAPH tag is set to YES then doxygen will show the
 # dependencies a directory has on other directories in a graphical way. The
@@ -2306,7 +2306,7 @@ GRAPHICAL_HIERARCHY    = YES
 # The default value is: YES.
 # This tag requires that the tag HAVE_DOT is set to YES.
 
-DIRECTORY_GRAPH        = YES
+DIRECTORY_GRAPH        = NO
 
 # The DOT_IMAGE_FORMAT tag can be used to set the image format of the images
 # generated by dot. For an explanation of the image formats see the section
@@ -2383,7 +2383,7 @@ PLANTUML_INCLUDE_PATH  =
 # Minimum value: 0, maximum value: 10000, default value: 50.
 # This tag requires that the tag HAVE_DOT is set to YES.
 
-DOT_GRAPH_MAX_NODES    = 10000
+DOT_GRAPH_MAX_NODES    = 100
 
 # The MAX_DOT_GRAPH_DEPTH tag can be used to set the maximum depth of the graphs
 # generated by dot. A depth value of 3 means that only nodes reachable from the
@@ -2395,7 +2395,7 @@ DOT_GRAPH_MAX_NODES    = 10000
 # Minimum value: 0, maximum value: 1000, default value: 0.
 # This tag requires that the tag HAVE_DOT is set to YES.
 
-MAX_DOT_GRAPH_DEPTH    = 0
+MAX_DOT_GRAPH_DEPTH    = 4
 
 # Set the DOT_TRANSPARENT tag to YES to generate images with a transparent
 # background. This is disabled by default, because dot on Windows does not seem
@@ -2431,4 +2431,4 @@ GENERATE_LEGEND        = YES
 # The default value is: YES.
 # This tag requires that the tag HAVE_DOT is set to YES.
 
-DOT_CLEANUP            = YES
+DOT_CLEANUP            = NO