Fix the typescript typings

- fix type for namedItem to be consistent with the flow types. The
  generic type applies to the return type, not to the form
- add support for refining the return type based on the constructor
  being passed as last argument, as done in flow types
- add testing of the typings, by running the typescript compiler on the
  test.ts file and ensuring that it does not complain about types. The
  refined return type is also now covered by this test.ts file.

Author: stof

index.d.ts

@@ -1,11 +1,11 @@
 export type Queryable = Document | DocumentFragment | Element;
 
-export function closest<T extends Element = HTMLElement>(context: Queryable, selectors: string, klass?: any): T;
+export function closest<T extends Element = HTMLElement>(context: Queryable, selectors: string, klass?: new() => T): T;
 
-export function query<T extends Element = HTMLElement>(context: Queryable, selectors: string, klass?: any): T;
+export function query<T extends Element = HTMLElement>(context: Queryable, selectors: string, klass?: new() => T): T;
 
-export function querySelectorAll<T extends Element = HTMLElement>(context: Queryable, selectors: string, klass?: any): Array<T>;
+export function querySelectorAll<T extends Element = HTMLElement>(context: Queryable, selectors: string, klass?: new() => T): Array<T>;
 
-export function namedItem<T extends HTMLFormElement = HTMLFormElement>(form: T, itemName: string, klass?: any): RadioNodeList | Element;
+export function namedItem<T extends Element | RadioNodeList = HTMLInputElement>(form: HTMLFormElement, itemName: string, klass?: new() => T): T;
 
 export function getAttribute(element: Element, attributeName: string): string;