docs: Initial refactoring of Metadata Chapter

Cleaning up the Metadata Chapter contents to wrap properly at 80
characters.

Signed-off-by: Bill Traynor <wmat@alphatroop.com>
docs: Reformatting xml to improve readability.

Reformatted user-manual-metadata.xml to 80 columns, as well
as improving the readability.

Signed-off-by: Bill Traynor <wmat@alphatroop.com>