Accept undefined as return value for before function.

Adds support for the `before` method to accept either a `true` or `undefined` return value to continue execution. This is preferred since functions by default return `undefined` if no return value is specified. We often forget to provide a return value in this `before` function and thus the Oform stops executing unintentionally. From now own if you want Oform to stop executing after the `before` function you must make the function return `false`.

The CI build is expected to fail. The CI environment still needs to be configured. I'm still running tests locally. Tests passing in Chrome, Firefox, Safari 7, IE11, IE10, and IE9.