Don't treat XML declarations as Processing Instructions

The XML declaration is not a processing instruction.

According to XML 1.0 (5th Edition), Section 2.6, the PI target names "xml",
"XML" and so on are reserved.

Production Rule 17 states:
> PITarget ::= Name - (('X' | 'x') ('M' | 'm') ('L' | 'l'))

This fixes #174.

sax.js

@@ -549,10 +549,11 @@ function parseDCC(source,start,domBuilder,errorHandler){//sure start with '<!'
 function parseInstruction(source,start,domBuilder){
 	var end = source.indexOf('?>',start);
 	if(end){
-		var match = source.substring(start,end).match(/^<\?(\S*)\s*([\s\S]*?)\s*$/);
+		var match = source.substring(start,end).match(/^<\?(\S+)\s*([\s\S]*?)\s*$/);
 		if(match){
-			var len = match[0].length;
-			domBuilder.processingInstruction(match[1], match[2]) ;
+			if(match[1].toLowerCase() !== 'xml'){//ignore XML declarations
+				domBuilder.processingInstruction(match[1], match[2]) ;
+			}
 			return end+2;
 		}else{//error
 			return -1;