Libgdata's port to meson is long due, and this MR is an effort to towards that direction. At the moment, a lot needs to be done given how vast libgdata is due to its different services and dependencies.
meson.build for the remaining sub directories and install the headers from those.
meson.build files to generate object files, executables and libraries.
liboauth to be the dependency. For some unknown reason, pkg-config can't find it in my system, albeirt ldconfig shows that it's installed.