#12 Change text/xml to application/xml

[Michael Good]

In the packaging specification, the references to the text/xml media type in sections 3.8.1 and 7.4 should be changed to the application/xml media type. The text/xml media type has several problems for OSF usage as discussed in RFC 3023. Its default of the US ASCII charset and forbidding of UTF-16 encoding are both problematic for international musical repertoire. In addition, the various OSF XML files are not intended to be readable by casual users. The Dolet 4.7 for Finale plug-in already uses application/xml in all places where an XML media type is required.