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 Job ID Name Coverage
  Test
passed #21584
VS2013
VS2013-32-bit

00:00:50

passed #21583
VS2013
VS2013-64-bit

00:00:53

passed #21582
VS2015
VS2015-32-bit

00:00:59

passed #21581
VS2015
VS2015-64-bit

00:01:08

passed #21575
Linux
clang-c++11

00:02:28

passed #21577
Linux
clang-c++98

00:01:54

passed #21580
Linux
cppcheck

00:01:46

passed #21585
Linux
doc

00:00:15

passed #21574
Linux
gcc-c++11

00:03:40

passed #21576
Linux
gcc-c++98

00:02:42

passed #21578
Apple
macos-c++11

00:01:23

passed #21579
Apple
macos-c++98

00:01:19