Can we document the AtExit function for addons?

[JCMais]

The function AtExit act as a module shutdown callback, and was added in this commit bnoordhuis/node@1c20cac, but was never documented (why?).

I'm pretty sure many addon developers wanted something like that, but probably never used that function because it is not documented anywhere.

There is a pull request here with documentation, but it was not merged into node for unknown reasons.

[brendanashworth]

for reference, e4a8d26 is the io.js equivalent commit. also, if you'd like to use the same change as that noted pull request, you could take the commits within and resubmit them here - typically pull requests provide better discussion over whether or not something should be added than just an issue.

[bnoordhuis]

Fixed by 98649fd.