Adding SPM Support

- Added SPM support. Once added to a project, the package can be imported the same way as you would with Cocoapods (`import MDFTextAccessibility`)
- There are no changes to the file structure or Cocoapods related files.

Closes #37

COPYBARA_INTEGRATE_REVIEW=#37 from oncallhealth:db/swiftpackagemanager bd0382d
PiperOrigin-RevId: 359779079

Author: DomenicBianchi01

Package.swift

@@ -0,0 +1,33 @@
+// swift-tools-version:5.3
+
+// Copyright 2020-present the Material Text Accessibility for iOS authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import PackageDescription
+
+let package = Package(
+    name: "MDFTextAccessibility",
+    platforms: [
+        .iOS("8.0"), .tvOS("9.0")
+    ],
+    products: [
+        .library(name: "MDFTextAccessibility", targets: ["MDFTextAccessibility"])
+    ],
+    targets: [
+        .target(
+            name: "MDFTextAccessibility",
+            path: "src",
+            publicHeadersPath: ".")
+    ]
+)