Prepare corundrum for release via Vagrant Cloud

- Update README to point to v2 docs
- Switch to librarian-chef gem
- Switch to .ruby-version/.ruby-gemset over .rvmrc
- Install base box from Vagrant Cloud
- Strip installed packages:
  - Install curl via shell provisoning
  - Install RVM via shell provisioning script
  - Install Ruby 2.1.1 via shell provisioning script
  - Drop legacy Ruby versions
  - Drop PostgreSQL until it can be properly implemented
  - Drop Node
Fix install permissions for RVM