Fix invalid XML in <iref> elements.
Replace '&' characters with entities.
Add missing semi-colons on entities
Fix invalid XML in <sref> elements.
Fix invalid doctype
Fix invalid XML comments.

"--" is not allowed inside comments:
http://en.wikipedia.org/wiki/XML#Comments
Attribute values must be in quotes
Merge pull request #14 from jwakely/invalid-xml

Fix invalid xml