Fix memilio logo in doxygen documentation (#926)

Author: reneSchm

docs/Doxyfile

@@ -821,7 +821,7 @@ EXAMPLE_RECURSIVE      = NO
 # that contain images that are to be included in the documentation (see the
 # \image command).
 
-IMAGE_PATH             =
+IMAGE_PATH             = ../docs/memilio-small.png
 
 # The INPUT_FILTER tag can be used to specify a program that doxygen should
 # invoke to filter for each input file. Doxygen will invoke the filter program