Change default apodization to C1

[ykyohei]

The docstring says we apodize by cosine taper but I have realized that it has not been standard one.
I'm not sure if it's okay to change the default, but this PR changes the default to standard cosine taper (hann window).

if apo_type == 'C1':
    cosedge = 0.5 * (np.cos(np.linspace(0, np.pi, apodize_samps)) + 1)
elif apo_type == 'old_default':
    cosedge = np.cos(np.linspace(0, np.pi/2, apodize_samps))

The calculation of weight_for_signal for hwpss and azss were redundant as get_apodize_window_from_flags.
They are simplified.

[msilvafe]

Thanks for correcting and simplifying. I didn't realize we were doing something non-standard!

Just one inline comment about docstrings.