Hi,

this is a complete (and clean) rewrite of my package [vc-use-package],
in order to properly integrate it with the Emacs core.  Basically, it
adds a new :vc keyword so one can leverage the 'package-vc-install*'
function(s) from within a use-package declaration.  For example,
specifying

    (use-package foo
      :vc (:url "bar")) 

would expand to (more or less, concentrating on the relevant part)

    (unless (package-installed-p 'foo)
      (package-vc-install '(foo :url "bar") nil))

This makes installing packages from remote sources a breeze.  There is
also support, via 'package-vc-install-from-checkout', for installing
local packages by additionally specifying a load path:

    (use-package foo
      :vc bar             ; optional name, use t or nil for foo
      :load-path "/path")
  ⇔
    (progn (eval-and-compile (add-to-list 'load-path <<path>>))
           (unless (package-installed-p 'bar)
             (package-vc-install-from-checkout <<path>> "bar"))
           …)

I don't know what the policy here is regarding sending multiple patches
in the same email, but since the second one is just adding
documentation, I didn't deem it "worth" a second mail.  Sorry (and do
let me know!) if this is disruptive to anyone.

Best,
  Tony

[vc-use-package]: https://github.com/slotThe/vc-use-package