Minor API and Webhook updates to better enable full circle interactions

[jesse]

Today we've released a few minor updates that have some powerful
implications for your development efforts. As listed in the changelog:
http://www.mailchimp.com/api/changelog.php

** mod: v1.2: listUpdateMember, listMemberInfo, listUnsubscribe, and
campaignEmailStatsAIM all accept the email "id"
in place of the email address. The "id" is easy to
access in Campaigns and is returned by Webhooks
and the listMemberInfo functions.
** mod: v1.2: if the list member unsubscribed from a campaign,
listMemberInfo will now return that campaign_id
* Webhooks: if the list member unsubscribed from a campaign, the
"unsubscribe" Webhook will now include that.

The basic point of those changes is to give you better options for the
development of full-circle interactions based on data exposed in your
Campaign and required by various API methods.