Add and use new HTMLMetadataDownloader. Fix #4414.

Core/Sources/Core/FoundationExtras/Date+Extensions.swift

@@ -0,0 +1,37 @@
+//
+//  Date+Extensions.swift
+//  RSCore
+//
+//  Created by Brent Simmons on 6/21/16.
+//  Copyright © 2016 Ranchero Software, LLC. All rights reserved.
+//
+
+import Foundation
+
+public extension Date {
+
+	// Below are for rough use only — they don't use the calendar.
+
+	func bySubtracting(days: Int) -> Date {
+		return addingTimeInterval(0.0 - TimeInterval(days: days))
+	}
+
+	func bySubtracting(hours: Int) -> Date {
+		return addingTimeInterval(0.0 - TimeInterval(hours: hours))
+	}
+
+	func byAdding(days: Int) -> Date {
+		return addingTimeInterval(TimeInterval(days: days))
+	}
+}
+
+public extension TimeInterval {
+
+	init(days: Int) {
+		self.init(days * 24 * 60 * 60)
+	}
+
+	init(hours: Int) {
+		self.init(hours * 60 * 60)
+	}
+}