Clone only latest version of builpacks

You dont need the buildpack history, so save bandwith and space
Myself (alanjds) added to AUTHORS
AUTHORS got alphabetical again
include libmagiclwand-dev to get magick wand headers
use the libmagickcore-dev which is a dependeecy of magicwand
Merge pull request #20 from alanjds/patch-1

Clone buildpacks with --depth=1
Merge pull request #21 from nolman/master

update packages so that rmagick can install
Merge branch 'master' of https://github.com/progrium/buildstep