Remove hard-coded offset of popup menu.

Instead of relying on offset values, align the top-right of the menu
with bottom-right of the Docs app title.

Fixes #516
Improve --import option docs.

Fixes #515
Basic auto-detect for Ext.define(function) syntax.

A patch by Patrick Gleichmann.

Specs by me.

Refs #527
Specify required Ruby version in gemspec.

Refs #536