Improve type of HandlebarsTemplateDelegate

Adds an optional type argument that should be useful for .hbs.d.ts files.

The RuntimeOptions were specified by looking at https://github.com/wycats/handlebars.js/blob/680ec96/lib/handlebars/runtime.js#L131-L171 -- these don't seem to be documented anywhere.

types/handlebars/index.d.ts

@@ -96,8 +96,8 @@ interface HandlebarsTemplatable {
     template: HandlebarsTemplateDelegate;
 }
 
-interface HandlebarsTemplateDelegate {
-    (context: any, options?: any): string;
+interface HandlebarsTemplateDelegate<T = any> {
+    (context: T, options?: RuntimeOptions): string;
 }
 
 interface HandlebarsTemplates {
@@ -108,6 +108,14 @@ interface TemplateSpecification {
 
 }
 
+interface RuntimeOptions {
+    partial?: boolean;
+    depths?: any[];
+    helpers?: { [name: string]: Function }
+    partials?: { [name: string]: HandlebarsTemplateDelegate }
+    decorators?: { [name: string]: Function }
+}
+
 interface CompileOptions {
     data?: boolean;
     compat?: boolean;