Add template library loading from FileSystem

Sources/HummingbirdMustache/Library+FileSystem.swift

@@ -0,0 +1,23 @@
+import Foundation
+
+extension HBMustacheLibrary {
+    func loadTemplates(from directory: String, withExtension extension: String = "mustache") {
+        var directory = directory
+        if !directory.hasSuffix("/") {
+            directory += "/"
+        }
+        let extWithDot = ".\(`extension`)"
+        let fs = FileManager()
+        guard let enumerator = fs.enumerator(atPath: directory) else { return }
+        for case let path as String in enumerator {
+            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 }
+            
+            // drop ".mustache" from path to get name
+            let name = String(path.dropLast(extWithDot.count))
+            register(template, named: name)
+        }
+    }
+}

Sources/HummingbirdMustache/Library.swift

@@ -1,9 +1,14 @@
 
 public class HBMustacheLibrary {
-    init() {
+    public init() {
         self.templates = [:]
     }
     
+    public init(directory: String) {
+        self.templates = [:]
+        self.loadTemplates(from: directory)
+    }
+    
     public func register(_ template: HBMustacheTemplate, named name: String) {
         templates[name] = template
     }