Merge branch 'fix_doxygen' into 'master'

Fix doxygen

See merge request !16
12 jobs for master in 3 minutes and 41 seconds (queued for 1 second)
Status Name Job ID Coverage
  Test
passed clang-c++11 #21575
Linux

00:02:28

passed clang-c++98 #21577
Linux

00:01:54

passed cppcheck #21580
Linux

00:01:46

passed doc #21585
Linux

00:00:15

passed gcc-c++11 #21574
Linux

00:03:40

passed gcc-c++98 #21576
Linux

00:02:42

passed macos-c++11 #21578
Apple

00:01:23

passed macos-c++98 #21579
Apple

00:01:19

passed VS2013-32-bit #21584
VS2013

00:00:50

passed VS2013-64-bit #21583
VS2013

00:00:53

passed VS2015-32-bit #21582
VS2015

00:00:59

passed VS2015-64-bit #21581
VS2015

00:01:08