TODO
====

  * Enable per-feed adjustments

    The goal is to better cope with feeds that don't have dates or ids or
    consitently encode or escape things incorrectly.

  * Expire feed history

    The feed cache doesn't currently expire old entries, so could get
    large quite rapidly.  We should probably have a config setting for
    the cache expiry, the trouble is some channels might need a longer
    or shorter one than others.

  * Allow display normalisation to specified timezone

    Some Planet admins would like their feed to be displayed in the local
    timezone, instead of UTC.