Add template library loading from FileSystem

Tests/HummingbirdMustacheTests/LibraryTests.swift

@@ -0,0 +1,18 @@
+import XCTest
+@testable import HummingbirdMustache
+
+final class LibraryTests: XCTestCase {
+    func testDirectoryLoad() throws {
+        let fs = FileManager()
+        try fs.createDirectory(atPath: "./templates", withIntermediateDirectories: false)
+        let mustache = "<test>{{#value}}<value>{{.}}</value>{{/value}}</test>"
+        let data = Data(mustache.utf8)
+        defer { XCTAssertNoThrow(try fs.removeItem(atPath: "templates")) }
+        try data.write(to: URL(fileURLWithPath: "templates/test.mustache"))
+        defer { XCTAssertNoThrow(try fs.removeItem(atPath: "templates/test.mustache")) }
+        
+        let library = HBMustacheLibrary(directory: "./templates")
+        let object = ["value": ["value1", "value2"]]
+        XCTAssertEqual(library.render(object, withTemplateNamed: "test"), "<test><value>value1</value><value>value2</value></test>")
+    }
+}