[Chicken-users] Changing the chickadee home page to C5

[John Cowan]

Currently chickadee.call-cc.org and api.call-cc.org redirect to api.call-cc.org/4/doc.  This grows more inappropriate with every new release of Chicken 5, indeed with every day that passes.  It's time to change it, I think, to redirect to api.call-cc.org/5/doc instead.

In addition, there should be reciprocal links between /4/doc and /5/doc.