Displays a color scale (HTML)

    Parameters:
    -----------
            scale : str
                    Color scale name
                    If no scale name is provided then all scales are returned
                            (max number for each scale)
                    If scale='all' then all scale combinations available 
                            will be returned

    Example:
            scales('accent')
            scales('all')
            scales()

def scales(scale=None):
    """
    Displays a color scale (HTML)

    Parameters:
    -----------
            scale : str
                    Color scale name
                    If no scale name is provided then all scales are returned
                            (max number for each scale)
                    If scale='all' then all scale combinations available 
                            will be returned

    Example:
            scales('accent')
            scales('all')
            scales()
    """
    if scale:
        if scale == 'all':
            display(HTML(cl.to_html(_scales)))
        else:
            display(HTML(cl.to_html(get_scales(scale))))
    else:
        s = ''
        keys = list(_scales_names.keys())
        keys.sort()
        for k in keys:
            scale = get_scales(k)
            s += '<div style="display:inline-block;padding:10px;"><div>{0}</div>{1}</div>'.format(
                k, cl.to_html(scale))
        display(HTML(s))