Merge branch 'doc' into 'devel'

.gitlab-ci.yml

CMakeLists.txt

README.md

doc/Doxyfile.in

doc/DoxygenLayout.xml

doc/conf.py

doc/index.rst

psrdada_cpp/dada_db.hpp

psrdada_cpp/dada_read_client.hpp

psrdada_cpp/dada_write_client.hpp

psrdada_cpp/double_buffer.cuh

psrdada_cpp/effelsberg/edd/EDDPolnMerge.hpp

psrdada_cpp/effelsberg/edd/EDDRoach.hpp

psrdada_cpp/effelsberg/edd/EDDRoach_merge.hpp

psrdada_cpp/effelsberg/edd/FftSpectrometer.cuh

psrdada_cpp/effelsberg/edd/GatedSpectrometer.cuh

psrdada_cpp/effelsberg/edd/GatedStokesSpectrometer.cuh

psrdada_cpp/effelsberg/edd/Tools.cuh

psrdada_cpp/effelsberg/edd/VLBI.cuh

psrdada_cpp/effelsberg/edd/src/vdif_send.cu