Fixes #225 - Use a properly defined user agent

* Set a proper user agent
* Add fallback when UA comes out nil
* Remove unused Bundle extension
* Return nil when asciification fails
* Add whitespace handling and further emoji test case
* Explicitly check if string is already in ASCII
* Rename factory to builder
* Use allSatisfy instead of reduce
* Use key path syntax

project.yml

@@ -45,6 +45,9 @@ packages:
   AppAuth:
     url: https://github.com/openid/AppAuth-iOS
     majorVersion: 1.5.0
+  DeviceKit:
+    url: https://github.com/devicekit/DeviceKit
+    majorVersion: 4.7.0
   DTCoreText:
     url: https://github.com/Cocoanetics/DTCoreText
     majorVersion: 1.6.26