Structure 'action' as a ConfirmAction on a HttpActionHandler in an EmailMessage.

Markup the action transactional template as an [EmailMessage][1], containing a
[HttpActionHandler][2] with a [ConfirmAction][3], giving the template direct
actionability via [Schema Actions][4].

Markup is in microdata, using chiefly the [schema.org][5] schema.

In addition, this implementation uses Gmail's [Actions in the Inbox][6] schema, which
predates and varies from Schema.org v1.2's implementation of [Schema.org Actions][4].
The [HttpActionHandler][2] property used here appears in the [Schema.org Actions
(Minimal Draft) spec][7], and made it in modified form (as HttpHandler) into [Actions
in schema.org - draft 4][8], before a subsequent reduction in [draft 6][9] to
EntryPoint that we see in the [latest April 11th revision][10] of [Schema Actions][4]
that was released in [Schema.org 1.2][4]. For further information Schema.org actions,
see: [http://www.w3.org/wiki/WebSchemas/ActivityActions][11].

The author expects Gmail will eventually comply with schema.org.

[1]: http://schema.org/EmailMessage
[2]: https://developers.google.com/schemas/reference/types/HttpActionHandler
[3]: http://schema.org/ConfirmAction
[4]: http://blog.schema.org/2014/04/announcing-schemaorg-actions.html
[5]: http://schema.org
[6]: https://developers.google.com/gmail/actions/
[7]: http://www.w3.org/wiki/images/7/79/Schema.orgActionsMinimaldraft.pdf
[8]: http://www.w3.org/wiki/images/b/b9/Actionsinschema.org.pdf
[9]: https://www.w3.org/wiki/images/7/7e/Actions-draft6.pdf
[10]: https://www.w3.org/wiki/images/1/10/PotentialActionsApril11.pdf
[11]: http://www.w3.org/wiki/WebSchemas/ActivityActions