Allow to store arbitrary files in .chef-runner folder

By changing sandbox path to .chef-runner/sandbox
Support global Vagrant machine IDs

By storing per-machine ssh config in .chef-runner/vagrant instead of
.vagrant.
Merge pull request #9 from mlafeldt/vagrant-global-ids

Support global Vagrant machine IDs
Document support of Vagrant machine UUIDs
Kick off development of v0.4.0
Show error message of `vagrant ssh-config` in case it fails
Build download archives for popular Unix systems

I doubt that Windows is supported at the moment.
Pass exact Git version to compiler

Inspired by https://github.com/mitchellh/packer/blob/master/packer/version.go
Add usage text
One build folder per version
Merge pull request #10 from mlafeldt/build

Build download archives
Split up prepareCookbooks method
Pass multiple path elems to SandboxPathTo and RootPathTo
Use Librarian-Chef if Cheffile exists
Rename Install to InstallCookbooks
Remove temporary Librarian-Chef files from destination
Consistent naming
Add Librarian-Chef to docs
Merge pull request #11 from mlafeldt/librarian

Support Librarian-Chef
Show program version with -version