Vote on Issues

I created a new page of the site, /issues, which pulls in the open Github issues for the Pullup project, and allows members to vote on those issues.

Eventually it would be nice to have everything integrated so that we can pull in Github comments (maybe even do threading), and post comments from Pullup, but I thought this might be a good start, and the voting should be useful almost immediately.

The prominent visibility will also make it very easy for newcomers to the site to find high priority things to work on.

This idea was originally mentioned by @chall8908 in #98.