How to update the directory structure of porters-handbook in zh_TW

[Warren Block]

On Thu, 10 Dec 2015, RayCherng Yu wrote:

> I remove it,too. I update a new diff.
> 
> What does the "IMAGES_LIB+=" mean? In my old Makefile, there are 1.png to 10.png but in the new Makefile, spanish version, there are 1.png to 21.png.

IMAGES_LIB is used to point to the callout images.  The current English 
Porter's Handbook security section uses these callout images:
https://www.freebsd.org/doc/en_US.ISO8859-1/books/porters-handbook/security-notify.html#security-notify-vuxml-db