UTF-8 view optimizations + Regression fix for #275 (#276)

* fix most tests

* utf-8 optimization

* fix regressions introduced by #275

Author: aehlke

Package.swift

@@ -4,6 +4,7 @@ import PackageDescription
 
 let package = Package(
     name: "SwiftSoup",
+    platforms: [.macOS(.v10_15), .iOS(.v13), .watchOS(.v4)],
     products: [
         .library(name: "SwiftSoup", targets: ["SwiftSoup"])
     ],