Convert nested arrays into DOMDocument

The extension converts nested PHP arrays and objects into DOMDocument.
Some of projects use XSLT as a templating engine. To build XML for such engines,
we need a very fast and memory efficient way to convert PHP nested arrays and
objects into DOMDocument object. Also, produced XML should be straight-forward
and as simple as it could be (BTW XMLRPC, SOAP and other XML-based formats are quite
sloppy in this case). So dom_varimport has been introduced: it produces DOMDocument
from a nested array near 20 times faster than a hand-made code in native PHP
(1 MB XML with thousands of nodes could be generated in 1-2 ms).