Accessibility support: keyboard navigation

Feature request to support functional accessibility for users with disabilities through [WCAG 2.0](https://www.w3.org/WAI/WCAG20/glance/) (meeting at least Level A, although Level AA would be great).

A lot of sites may need to comply with regulations or accessibility mandates for their user population. Organizations may also want to proactively accommodate users with disabilities to allow content to be consumed by everyone. This can influence the decision for developers in selecting particular libraries or approaches in presenting data to users.

An example scenario would be with the Americans with Disabilities Act (ADA). It would be legally considered discrimination if, as an example, a sighted employee became blind and the employer did not accommodate the employee to allow them to do their job.

This request is not really asking for ensuring entire compliance, as things like contrast ratio of colors would be the responsibility of developer creating the chart, but more looking for support for screen readers, keyboard navigation, and similar functional and structural areas.