Updated #build_token method to be a public method.
Updated #build_token method to be a public method.

- Allows one to forcibly build the token rather than wait for
  before validation callbacks to fire.
- Avoids the bad practice of calling #valid? as a workaround to build
  the token.

bkuhlmann/tokener,bkuhlmann/tokener,bkuhlmann/tokener