Moving toward DOM framework
Upgrades to Element class

* Added "xlink" group of attributes
* Now underscores in element properties are automatically converted to
hyphens
Update Image and Tspan classes

Bring both in line with DOM implementation
Created todo list for package migration
Merge branch 'dom-rewrite' of https://github.com/memethief/XML_SVG into dom-rewrite

Conflicts:
	XML/SVG/Document.php
	XML/SVG/Element.php
	XML/SVG/Group.php
	XML/SVG/Image.php
	XML/SVG/Path.php
	XML/SVG/Rect.php
	XML/SVG/Text.php
	XML/SVG/Tspan.php