Update user guide documentation:

- Remove style guide from user guide; moved to doxygen manual.
- Replace with improved introduction for developers and packagers.
- Move introductory paragraph about the project under the About page.


git-svn-id: svn://svn.berlios.de/openocd/trunk@1895 b42882b7-edfa-0310-969c-e2dbd0fdcd60