[boost] [GIL] Pixel Layout Padding?

Hi there, The current gil::pixel design has a deficiency that you can't specify the align of pixel, for example, you can't have an RGBX pixel in GIL where X is padding. An alternative is to introduce a dummy channel for X, but that doesn't seem to be a good idea as we don't want to mess up the color space. So, maybe it'd be better to extend the current design, say, pixel<ChannelValue, Layout>, to something like pixel<ChannelValue, Layout, Align>. Then we can specify RGBX as pixel<uint8_t, rgb_layout_t, 4>, or XRGB as pixel<uint8_t, rgb_layout_t, -4> where minus means left justify. Ideas?