#28 e-mail notification in digest mode

[Giovanni Bajo]

Hello,

e-mail notifications are very useful, but they can
generate too many mails if the Wiki is active (if one
subscribes to many pages).

One solution could be to have a digest mode: instead of
sending an e-mail immediatly, the modifies are batched
together and a single mail listing all of them is generated
every N hours (twice a day for instance).