Add working Jest & TypeScript config

- Jest now uses ts-jest for transforms
- TypeScript compilation via `lerna run tsc`

__tests__/github.test.ts

@@ -0,0 +1,7 @@
+import { github } from '../src/github';
+
+describe('@actions/github', () => {
+  it('needs tests', () => {
+      expect(github()).toBe(true)
+  });
+});