updated the website documentation to reflect 2.2.4 instead of 2.3

Had a hard time finding xdebug 2.3, so I pulled down all the code and saw that all these changes are actually in 2.2.4.  I figured I could help out by sending in a pull request to update the docs. The only one I wasnt 100% sure on was the trace_format changes.  Also I have no idea whats going on with line 36/37 in xdebug_debug_zval - maybe an encoding issue or something.