gm_planar docstring normal vector unclear

[mducle]

The gm_planar docstring is slightly misleading. It says:

% `[s, k, n, name, pname, limit] = gm_planar(S0, x)` generates the
% parameters of arbitrary planar magnetic structure from $\varphi$ angles
% (in radian), ordering wave vector (rlu) and spin plane normal vector
% ($xyz$).

but actually the normal vector is not given as two angles n_theta and n_phi which are not clearly defined. It should be updated to say that these are spherical polar angles with respects to the crystal Cartesian coordinate system, where n_theta is the azimuthal angle away from the crystal Cartesian z axis, and n_phi is the angle in the x-y plane away from x. Thus x is specified as n_theta=90, n_phi=0 whilst z is n_theta=0, n_phi=0 and y is n_theta=90, n_phi=90.