Added support for internationalization (i18n)

This is a major version. I completed the support for i18n methods in the
Sandbox API:
- i18n.getLanguageList()
- i18n.getSelectedLanguage()
- i18n.selectLanguage()
- i18n.addLanguageProperties()
- i18n.get()
- i18n.getString()
- i18n.filterHtml()

Also, new in this version:
- added HTML index file in doc/ as entry point to the documentation
- enhancements and bug fixes in base modules for i18n and templates
- added hasAttribute() and constants in base dom module

In the next major version, I plan to add support for plugins to the Sandbox API
which should make it easier to extend and customize the API for the specific
needs of an application. I also intend to document the different extension
points of the library:
- configuration properties and custom factory
- custom modules with a custom sandbox
- Sandbox API plugins

README.txt

@@ -155,6 +155,6 @@ HISTORY
   2010-10-26, v1.4.0, Added confirm method in sandbox.utils API
   2010-12-20, v1.4.1, Refactored base i18n API: simpler yet powerful
   2010-12-20, v1.4.2, Bug fix: language code comparison is now case-insensitive
-  2010-XX-XX, v1.5.0, ROADMAP: add support for internationalization (i18n)
-  2010-XX-XX, v1.6.0, ROADMAP: add support for plugins to extend Sandbox API
+  2011-01-05, v1.5.0, Added support for internationalization (i18n)
+  2011-XX-XX, v1.6.0, ROADMAP: add support for plugins to extend Sandbox API