Having an output of '.' means the $builddir/doc directory was removed on ninja
clean, only for ninja to then fail because doc/libei.h wasn't there. Let's use
the reference from meson test cases itself.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Build the doxygen API documentation. This is copied from libinput so it takes
over that style (which is more readable than the default doxygen style).
Some extra documentation is added too and all the immediate errors are fixed
in this commit but doxygen still warns about undocumented parameters.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
