Update 'yungsang/boot2docker' to version 1.0.0
Add shared dir './data', ignoring contents; fix #1

Vagrant tries to share this folder with the VM and errors if missing.
Make shared dir location configurable via ENV vars

* VAGRANT_B2D_SHARE_NAME - shared dir name
* VAGRANT_B2D_SHARE_ROOT - path parent of shared dir relative `vagrant-haskell`
Add documentation for VAGRANT_B2D_GUI to README.md
Refactor: whitespace
Document 'get_cpus' and 'get_ram' functions
Update docs to reflect commands in vagrant-haskell
Document how to halt the Docker container host VM