Documentation/parport.txt: convert to ReST markup

- Add a document title;
- use quote blocks where needed;
- convert parameters to a nested table;
- use monotonic fonts for config options and file names;
- adjust whitespaces and blank lines;
- replace _foo_ by **foo**;
- add it to the user's book.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>