Rename package to swift-mustache (#27)

* Rename package to swift-mustache

* Update CI

Sources/Mustache/CustomRenderable.swift

@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Hummingbird server framework project
+//
+// Copyright (c) 2021-2021 the Hummingbird authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See hummingbird/CONTRIBUTORS.txt for the list of Hummingbird authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+
+/// Allow object to override standard hummingbird type rendering which uses
+/// `String(describing)`.
+public protocol MustacheCustomRenderable {
+    /// Custom rendered version of object
+    var renderText: String { get }
+    /// Whether the object is a null object. Used when scoping sections
+    var isNull: Bool { get }
+}
+
+extension MustacheCustomRenderable {
+    /// default version returning the standard rendering
+    var renderText: String { String(describing: self) }
+    /// default version returning false
+    var isNull: Bool { false }
+}
+
+/// Extend NSNull to conform to `MustacheCustomRenderable` to avoid outputting `<null>` and returning
+/// a valid response for `isNull`
+extension NSNull: MustacheCustomRenderable {
+    public var renderText: String { "" }
+    public var isNull: Bool { true }
+}