Regardless of dependencies, `fig up` only attaches to what you specify

Without this, if you go:

    $ fig up -d db
    $ fig up web

you'll get output for both db and web, and Ctrl-C will kill them both.

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>
Merge pull request #308 from orchardup/fix-fig-up-attach

Regardless of dependencies, `fig up` only attaches to what you specify
Add docs for volumes_from

Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Ship 0.5.0

Signed-off-by: Ben Firshman <ben@firshman.co.uk>