artwork-archive

Previous to this commit, paths passed to Docbook external references
inside Docbook documentation models pointed to files under a trunk/
directory.

In this commit, I remove the trunk/ part from paths. It is no longer
needed when we use a Git repository layout. To remove the trunk parth
from paths I used the following commands:

 - sed -i -r 's!trunk/!!g' $(find Documentation/Models/Docbook -name '*.docbook')
 - sed -i -r 's!trunk/!!g' $(find Documentation/Models/Docbook -name '*.ent')

The change committed here may introduce incoherences to contents
inside documentation manuals written in Docbook format that need to be
fixed.

In addition to change committed here, the following Docbook entities
were also added along with it to Tcar-ug documentation manual:

 - TCL: The CentOS Logo
 - TCS: The CentOS Symbol
 - TCT: The CentOS Type
 - TCB: The CentOS Brand