Enhancements to localized_country_select_tasks.rake

1. Support .yml as output format (default is Ruby as per existing behavior) via FORMAT parameter.
2. Auto-convert user locale to Unicode.org CLDR acceptable code. This magic can be overriden by WEB_LOCALE parameter.
3. Output file name will be "countries.<locale>.<format>" in keeping with conventions of other ruby/rails i18n libraries