Check values of @meiversion

Check what is about values like ```meiversion="2013"``` in files ```mei_to_html.xsl```, ```view_score.xq```, and ```bibl_reference_types.xml```.

From MEI Guidelines, the legit values are: ```3.0.0```, ```4.0.0```, ```4.0.1```, ```5.0```, ```5.0+anyStart```, ```5.0+basic```, ```5.0+CMN```, ```5.0+Mensural```, and ```5.0+Neumes```. 