Correcting deprojection problems

[j6626]

The current version of the deprojection function fills in NaNs with

        r = np.where(np.isfinite(r_obs), r_obs, rf)
        t = np.where(np.isfinite(t_obs), t_obs, tf)
        z = np.where(np.isfinite(z_obs), z_obs, zf)

However, this creates a discontinuous grid at sufficiently high inclinations and leads to the addition of artificial disk components. I removed these lines and added np.nan_to_num calls around other functions that depend on r, t, and z. Since the current interpolation routine is leaving NaNs in the middle of the grid, I replaced it with SciPy's interpolation routine, which does not appear to exhibit the same issues.