a single documentation index for all installed paeckages

[krux02]

This is a feature request.

nimble should be able to generate a single index for all installed packages. The idea is that the index looks like theindex but it will be offline and it will include all packages that are installed via nimble.

when there are multiple versions installed of a single package, I think for the documentation just to have the newest version would be enough for the beginning.

Just as a reference the go programming language already does this: https://godoc.org/golang.org/x/tools/cmd/godoc

related issue: nim-lang/Nim#9444