RFC: let `paket pack` generate a `paket.local` snippet

Use Case

It becomes cumbersome to create/maintain paket.local for testing new features when
a) many packages are involved (as in large-scale software projects), and
b) version numbers changes often (as in continuous deployment scenarios, especially when using GitVersion or similar)

Proposal

Provide an additional parameter for paket pack, e.g. --generate-paket-local, to create a paket.local file that references the nuget packages just build.

The file could be generated per default in the output directory and/or the new parameter provides the target file (i.e. --generate-paket-local=/some/dir/paket.local.inc).

Known workarounds

Right now we use some bash/sed magic to convert the paket pack-output into a paket.local snippet, i.e. piping into this bash function:

PAKET_LOCAL="nugets/paket.local.inc"
function extend_paket_local {
    while read -r line; do
        line="${line%"${line##*[![:space:]]}"}" # remove trailing whitespace
        echo -E "$line"
        if [[ "${line}" == 'Wrote: '* ]] && [[ "${line}" == *'.nupkg' ]]; then
            echo -E "${line}" | sed -r '
                s/^Wrote: (.*)\\([^\]+)\.([0-9]+\.[0-9]+\.[0-9]+(-[a-z][-a-z0-9]+)?)\.nupkg$/nuget \2 -> source "\1" version \3/
            ' >> "$PAKET_LOCAL"
        fi
    done
}

Start by locating the paket pack command implementation and its handling of written .nupkg files. Review the existing paket.local syntax and determine how the proposed option and output path should behave; done means generated output contains valid package references for the packages just built.