feat: Begins snapshot testing for html

Sources/HtmlSnapshotTesting/HtmlSnapshotTesting.swift

@@ -10,3 +10,13 @@ public extension Snapshotting where Value == (any HTML), Format == String {
     return snapshotting
   }
 }
+
+public extension Snapshotting where Value == String, Format == String {
+  static var html: Snapshotting {
+    var snapshotting = SimplySnapshotting.lines
+      .pullback { $0 }
+
+    snapshotting.pathExtension = "html"
+    return snapshotting
+  }
+}