HTML traces

Tracing only parts of an application with xdebug_start_trace() and xdebug_stop_trace().

Fetching the trace file name that is being used with xdebug_get_tracefile_name().

Changing how much data is shown with xdebug.var_display_max_children, xdebug.var_display_max_data and xdebug.var_display_max_depth.