BeautifulSoup instead of minidom

minidom is not very compliant with the (sometimes) invalid xml provided by mediainfo.

For example, minidom refuses the following xml countaining  '\&\#x01;', resulting in an empty MediaInfo.xml_dom

    '<?xml version="1.0" encoding="UTF-8"?>\n<Mediainfo><track type="General">...\n<segm>&#x01;</segm>\n</track>\n\n</Mediainfo>\n\n'

replacing minidom by BeautifulSoup permits to deal with this movie (and with many more).

This commit:
replaces minidom by BeautifulSoup
adds beautifulsoup4 requirement
bumps version number from 1.3.5 to 1.3.6