Split package: PkgGraph, PkgGraphViz

[tfiers]

Re

• make DepGraphs its own package? #107

When we split, we can keep version history in both. (This repo will be renamed to ..Viz. and then a new repo with this name will be created, haha).
(Keeping version history is good for General, with its versions: the old PkgGraph then included viz, newer versions no longer).

Question renaming: can we have both pkg i.e. module PkgGraph, and struct PkgGraph ? Don't think so? (And yeah, this is why pkgs are named in plural, but alas, not allowed to change name anymore:

Rejection of renamed pkg in General registry, as too similar name:

• New package: PkgGraphs v0.2.0 JuliaRegistries/General#74747

)

[tfiers]

(no, you can't do module X; struct X end; end: gives an error immediately: Invalid redefinition of constant X).

So, we'll have to name our struct (if we have one even) something else: PackageGraph, PkgWithDeps, ...