Document public api

[sorvell]

As a first documentation test, we should at least note and document public api.

[sorvell]

Specifically for components g-icon, g-icon-button, g-overlay, g-selector, g-selection

[sjmiles]

Yes, I suppose I've been waiting on that until I can actually use the markup to produce some document. Daniel says he's close to having something on that.

[frankiefu]

Work in progress, but closing since this work is underway...