Add swift-log so we can log loading errors

Sources/HummingbirdMustache/Library+FileSystem.swift

@@ -1,8 +1,9 @@
 import Foundation
+import Logging
 
 extension HBMustacheLibrary {
     /// Load templates from a folder
-    func loadTemplates(from directory: String, withExtension extension: String = "mustache") {
+    func loadTemplates(from directory: String, withExtension extension: String = "mustache", logger: Logger?) {
         var directory = directory
         if !directory.hasSuffix("/") {
             directory += "/"
@@ -14,8 +15,11 @@ extension HBMustacheLibrary {
             guard path.hasSuffix(extWithDot) else { continue }
             guard let data = fs.contents(atPath: directory + path) else { continue}
             let string = String(decoding: data, as: Unicode.UTF8.self)
-            guard let template = try? HBMustacheTemplate(string: string) else { continue }
-            
+            guard let template = try? HBMustacheTemplate(string: string) else {
+                logger?.error("Failed to load \(path)")
+                continue
+            }
+            logger?.debug("Loading \(path)")
             // drop ".mustache" from path to get name
             let name = String(path.dropLast(extWithDot.count))
             register(template, named: name)