cct: A few changes

* Change how end block is handled

  - the last indentation is computed from the indentation
    of the end keyword

  - closing all opened blocks is no longer needed
    and you need to close only the last block that
    needs to be closed

* Change how python sequences are handled

  - The format for prefix for Python sequences has been changed to
    "\s*@\s\" or simple "@"

    i.e. lines that start with @ that is not followed by whitespace
    are considered verbatim

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
Add HOWTO

Signed-off-by: Cyril Hrubis <metan@ucw.cz>