Standardise how examples are run

[Peter Monks]

Currently the examples are run in 2 different ways. It would be great to standardise on a single approach, to make it easier for newcomers to the library.

• 01 Hello world: (require '[getting-started.01-hello-word]) (note: (-main) is automatically invoked)
• 02 Form: (require '[getting-started.02-form :as form]) (form/-main)
• Shapes 3d: (require '[other-examples.shapes-3d :as shapes-3d]) (shapes-3d/-main)
• Todo: (require '[other-examples.todo :as todo]) (todo/-main)