prepare a base for i18n

Simply move translated pages to /LOCALE/ will cause:

- broken links
- broken images

This is because:

- The default layouts assume resources are located in the root
  directory.
- In content pages, some links link to the root directory also.

This commit fix the above problems and add a example of /LOCALE/,
i.e. /en/, which can be
used as the base for i18N.

See #68