v2.0.0

Bug Fixes:

• Use /run/ignition/dev_aliases instead of /dev_aliases when creating our
  own symlinks to devices in /dev

Test Changes:

• Rename tests to use dots.with.lowercase

Public Go API Changes:

• Replace config/validate api with github.com/coreos/vcontext
• Validate() functions in config/* now follow the vcontext validation interface