(PUP-2389) Add ruby 2.0.0-x64

 - This provides a vendored ruby 2.0.0-p481 based currently on the
    ruby installer for Windows.
 - Removes Tcl/Tk as they are not included as part of the standard
    install of ruby on Windows. This gives a savings of at least 10MB.
- Removes generated docs for gems freeing up 9MB.
Merge remote-tracking branch 'rob/ticket/2.0.0-x64/PUP-2389-ruby2' into 2.0.0-x64

* rob/ticket/2.0.0-x64/PUP-2389-ruby2:
  (PUP-2389) Add ruby 2.0.0-x64