refactor: TemplateLoader to protocol, follow Swift API guidelines

CHANGELOG.md

@@ -4,6 +4,12 @@
 
 ### Breaking
 
+- `TemplateLoader` is now a protocol with the file system based loader now
+  called `FileSystemLoader`. You will need to use `FileSystemLoader` instead.
+
+- `TemplateLoader` `loadTemplate` methods are now throwing and now take labels
+  for the `name` and `names` arguments.
+
 - Many internal classes are no longer private. Some APIs were previously
   accessible due to earlier versions of Swift requiring the types to be public
   to be able to test. Now we have access to `@testable` these can correctly be