Add selector initializer for creating instances with a given selector string

HTMLKit/CSSSelector.h

@@ -44,6 +44,7 @@ extern NSString * _Nonnull NSStringFromNthExpression(CSSNthExpression expression
 
 @interface CSSSelector : NSObject 
 
-- (BOOL)acceptElement:(nonnull HTMLElement *)element;
++ (nullable instancetype)selectorWithString:(NSString *)stirng;
+- (BOOL)acceptElement:(HTMLElement *)element;
 
 @end

HTMLKit/CSSSelector.m

@@ -8,9 +8,20 @@
 
 #import <Foundation/Foundation.h>
 #import "CSSSelector.h"
+#import "CSSSelectorParser.h"
 
 @implementation CSSSelector
 
++ (instancetype)selectorWithString:(NSString *)string
+{
+	NSError *error = nil;
+	CSSSelector *instance = [CSSSelectorParser parseSelector:string error:&error];
+	if (error) {
+		return nil;
+	}
+	return instance;
+}
+
 - (BOOL)acceptElement:(HTMLElement *)element
 {
 	[self doesNotRecognizeSelector:_cmd];