Add next.js flowtype definition to with-flow example (#973)

* Add next.js flowtype definition to with-flow

* Add render api types for flow

* Add prefetch types

* Fix push/replace api types to promise

examples/with-flow/.flowconfig

@@ -3,5 +3,6 @@
 [include]
 
 [libs]
+types/
 
 [options]

examples/with-flow/types/next.js.flow

@@ -0,0 +1,50 @@
+/* @flow */
+
+declare module "next" {
+  declare type NextApp = {
+    prepare(): Promise<void>;
+    getRequestHandler(): any;
+    render(req: any, res: any, pathname: string, query: any): any;
+    renderToHTML(req: any, res: any, pathname: string, query: string): string;
+    renderError(err: Error, req: any, res: any, pathname: any, query: any): any;
+    renderErrorToHTML(err: Error, req: any, res: any, pathname: string, query: any): string;
+  };
+  declare module.exports: (...opts: any) => NextApp
+}
+
+declare module "next/head" {
+  declare module.exports: Class<React$Component<void, any, any>>;
+}
+
+declare module "next/link" {
+  declare module.exports: Class<React$Component<void, {href: string}, any>>;
+}
+
+declare module "next/prefetch" {
+  declare export var prefetch: (url: string) => any;
+  declare export var reloadIfPrefetched: any;
+  declare export default Class<React$Component<void, {href: string, prefetch?: boolean}, any>>;
+}
+
+declare module "next/router" {
+  declare module.exports: {
+    route: string;
+    pathname: string;
+    query: Object;
+    onRouteChangeStart: ?((url: string) => void);
+    onRouteChangeComplete: ?((url: string) => void);
+    onRouteChangeError: ?((err: Error & {cancelled: boolean}, url: string) => void);
+    push(url: string, as: ?string): Promise<boolean>;
+    replace(url: string, as: ?string): Promise<boolean>;
+  };
+}
+
+declare module "next/document" {
+  declare export var Head: Class<React$Component<void, any, any>>;
+  declare export var Main: Class<React$Component<void, any, any>>;
+  declare export var NextScript: Class<React$Component<void, any, any>>;
+  declare export default Class<React$Component<void, any, any>> & {
+    getInitialProps: (ctx: {pathname: string, query: any, req?: any, res?: any, xhr?: any, err?: any}) => Promise<any>;
+    renderPage(cb: Function): void;
+  };
+}