[Orgmode] [babel] support plantuml

[zwz]

I came across Ian Yang's 
[[http://www.emacswiki.org/emacs/org-export-blocks-format-plantuml.el][org-export-blocks-format-plantuml]]
 a few days ago, which brought me in front of the
great software [[http://plantuml.sourceforge.net/][Plantuml]]. It is an 
open-source tool in java that allows to quickly write:
    - sequence diagram,
    - use case diagram,
    - class diagram,
    - activity diagram,
    - component diagram,
    - state diagram
    - object diagram

using a simple and intuitive language.

Although Ian Yang's code has incorporated plantuml in org-mode by =#+BEGIN_UML= 
and =#+END_UML=, I think it
should be a good idea to introduce the plantuml as a new language into 
org-babel.

Here is the "ob-plantuml.el":

ob-plantuml.el
Description: application/emacs-lisp

I am not sure if it is qualified to be part of org-babel, so I just put
it here first.

In addition, I also wrote a new major mode “plantuml-mode.el” which
provides preliminary font-lock function for plantuml scripts, see 
http://zhangweize.wordpress.com/.