Version Toolbelt update zip packages

Changes:
* rake scripts for pkg and exe file generation
  create the update packages with a version suffix:
  e.g. td-update-(zip|exe)-0.11.2.zip
* updater fetches the correctly named zip file from
  S3 using the toolbelt.treasuredata.com/version.(exe|pkg)
  version as reference
* the toolbelt.treasuredata.com site links to the
  correct version of the update zip file transparently

Implements CLT-322