refactor: TemplateLoader to protocol, follow Swift API guidelines

Sources/Template.swift

@@ -9,6 +9,12 @@ let NSFileNoSuchFileError = 4
 public class Template: ExpressibleByStringLiteral {
   let tokens: [Token]
 
+  /// Create a template with a template string
+  public init(templateString: String) {
+    let lexer = Lexer(templateString: templateString)
+    tokens = lexer.tokenize()
+  }
+
   /// Create a template with the given name inside the given bundle
   public convenience init(named:String, inBundle bundle:Bundle? = nil) throws {
     let useBundle = bundle ??  Bundle.main
@@ -25,28 +31,22 @@ public class Template: ExpressibleByStringLiteral {
   }
 
   /// Create a template with a file found at the given path
-  public convenience init(path:Path) throws {
+  public convenience init(path: Path) throws {
     self.init(templateString: try path.read())
   }
 
-  /// Create a template with a template string
-  public init(templateString:String) {
-    let lexer = Lexer(templateString: templateString)
-    tokens = lexer.tokenize()
-  }
-
   // Create a template with a template string literal
-  public convenience required init(stringLiteral value:String) {
+  public convenience required init(stringLiteral value: String) {
     self.init(templateString: value)
   }
 
   // Create a template with a template string literal
-  public convenience required init(extendedGraphemeClusterLiteral value:StringLiteralType) {
+  public convenience required init(extendedGraphemeClusterLiteral value: StringLiteralType) {
     self.init(stringLiteral: value)
   }
 
   // Create a template with a template string literal
-  public convenience required init(unicodeScalarLiteral value:StringLiteralType) {
+  public convenience required init(unicodeScalarLiteral value: StringLiteralType) {
     self.init(stringLiteral: value)
   }