Still Alpha on PyPI

[mivade]

webassets seems to be, for the most part, quite stable and widely recommended. However, it is still listed as in an "Alpha" state on PyPI. I have no idea if this actually affects anyone's decision to use it, but I think bumping the status to "Production/Stable" (or at worst "Beta") is a good idea.

Thank you, @miracle2k and contributors, for this great library!