Include Emacs version in package-user-dir
Make tests runnable
Do not hard-code elpa directory in ecukes tests

fixes all previously failed ecukes tests
Fix accidentally passing test
Document the new way of configuration in README
Add carton-initialize to simplify initialization
Fix invalid TODO comment
Change .carton/elpa/VER to .carton/VER/elpa

See the discussion in:
https://github.com/rejeep/carton/issues/31#issuecomment-19253414
Mention pallet in a different section in README
Merge branch 'versioned' into v0.4-wip (fixes #31)

Packages are now installed in `.carton/EMACS-VERSION/elpa` instead
of `elpa/`.  Ecukes tests are changed accordingly.  Unit tests are
not fixed as they are deprecated.

See also #40