Renamed README files and .plugin
Add support for some of Pygments' options.

- Register "code", "code-block", "sourcecode" & "sourcecode-block" as
  aliases to the same directive.
- Rewrite the "pygments_directive" function as a class (Pygments).
- Create a new formatter each time. It takes more time to format the
  document because of that, BUT :
- Add support for some of Pygment's formatting options :
  * linenos (as a flag)
  * hl_lines
  * linenostart
  * linenostep
  * linenospecial
  * nobackground (as a flag)
  * anchorlinenos (as a flag)
  * noclasses (as a flag)