xvidenc 8.2.3 released

* Small improvement to how the MKV XML tagging file gets exported. Also improved the XML formatting and added COMMENT string with text "Tagged by xvidenc $version" and added SOURCE entry
* Added comment tag for MP4 and OGM with the same text as above
* Small update to the video_deinterlace_func() function's menu
* Add comment header with dates to batch files
* Use only lowercase words in all case statements that deal with the input source
* Placed the -passlogfile option inside the PASSLOG variable
* Added support for 2-pass Nero AAC audio encoding. Note that 2-pass is only supported by ABR/CBR encoding and ensures that the output quality is constant (like VBR) while also ensuring that a specified output bitrate is achieved (like CBR)
* Small bugfix: the counter in set_output_filename_func() didn't increase itself
* Replaced variable $source with $type and $vtype with $source