Prefix function declarations with export keyword

Visible bugs:
- Method signatures stop rendering
- Method return type is not inferred from flow type.

Author: ajhyndman

src/index.js

@@ -4,7 +4,7 @@
  * @param a A number to be doubled
  * @returns The input number, doubled
  */
-function double (a: number): number {
+export function double (a: number): number {
   // Do some stuff
   return a * 2;
 }
@@ -15,7 +15,7 @@ function double (a: number): number {
  * @param a A number to be tripled
  * @returns The input number, tripled
  */
-function triple (a: number): number {
+export function triple (a: number): number {
   // Do some stuff
   return a * 3;
 }