integrate with github to figure out when issues are assigned or track other status

[nikomatsakis]

It would be nice if the skill trees could integrate with github to figure out assignment or other status. Right now, we just have a generic href link, but maybe they could check if the issue is assigned and create the appropriate emoji etc. (Or perhaps use other labels.)

In general, it might be nice to be able to move more and more of the metadata into issues, actually, such that this is more of a "view onto" github where people are following certain conventions than having a real toml file? Something to think about.