Compressed formats for glTexStorage*

[Botondar]

I know that the official refpages don't list the compressed formats for the glTexStorage* formats, but they're perfectly valid, so it might be a nice addition if they showed up in the docs.gl pages as well.

Although this might be pushing it, but it would be cool if (even though they're extensions) the S3TC formats showed up there as well, since they're so common and pretty much universally supported, as per this page.