Tweak fulfillment reminder

Remove the "you haven't sent any books in the last week" language, it
was somewhat off-putting.
Add a way to edit a pledge

This just lets you change the quantity.
Attempt to robustify tests

Some of these tests were failing intermittently (rarely) with an error
like:

<Thu, 18 Apr 2013 15:31:03 PDT -07:00> (256995000[ns]) expected but was
<Thu, 18 Apr 2013 15:31:03 PDT -07:00> (256994000[ns]).

I.e., off by 1 microsecond. Unclear what was causing this but I suspect
some rounding on save. So, now I grab the time after save in order to
compare it to the later value.
Add pledges to events so pledges can have events
Add update events to pledges
Log update events when pledges are updated
Add ability to cancel pledges (model layer)

Canceled pledges don't get reminders and (soon) won't show up in the app
where pledges currently show.
Add ability to cancel a pledge (controller layer)

Also, canceled pledges now don't show up on the profile page or donate
page.
Update/fix some broken fixture-based tests
Add a way to make a new pledge

If the current user is a donor but doesn't have a current pledge, we
show a link to the new-pledge form and let them make a new one.
Add pledge reference to donations

This is to track which donations went with which pledges, so that we
know when a given pledge has been fulfilled.
Show previous donation count for current pledge

On the donate page, in the sidebar.
Add support for ended pledges

Ended pledges are pledges whose time is up. Nothing actually ends
pledges yet, but soon we'll do that automatically.
Automatically end pledges and mail users

Ends active pledges after the PLEDGE_PERIOD of 1 month, emailing the
user with a summary of how they did and encouraging them to make a new
pledge.
Fix typo
Send users to donate page after pledging

Makes more sense than the homepage
Slight improvements to tests/factories
Support for recurring pledges

Pledges can now be recurring, in which case they are autorenewed when
they are ended. This sends a somewhat different email to the donor.
Take advantage of pledge_summary

Use this and feedback_for in the PledgeHelper to simplify and consistify
some code
Add radio buttons for recurring bit on pledges

Users can now choose "this month" vs. "every month" when creating or
updating a pledge, in order to set the recurring? bit.

Also DRY up the forms with a partial.