2.x.x Template struct (#22)

* Start of turning template into a struct

* Everything is Sendable now, just doesnt work

* Add library to context

* Make sure render is initialized with library

* comment about inheritance spec

* Add register back in

* Re-instate register functions

* Re-instate commented out print

* Fix tabbing in Partial tests

* Make HBMustacheLibrary.loadTemplates async

* Update platforms, swift version

Package.swift

@@ -1,10 +1,11 @@
-// swift-tools-version:5.3
+// swift-tools-version:5.7
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription
 
 let package = Package(
     name: "hummingbird-mustache",
+    platforms: [.macOS(.v10_15), .iOS(.v13), .tvOS(.v13), .watchOS(.v6)],
     products: [
         .library(name: "HummingbirdMustache", targets: ["HummingbirdMustache"]),
     ],