* Use good/bad votes in random picking
  - file hashing may take a long time to calculate, we may want
    a cached filename -> hash cache?

* Also account for last change time, avoid recently set wallpapers
  and especially the last one used.
  - If we're forced to, don't count as a switch.

* --newer option to restrict by modified time of wallpapers

* Splitting across multiple monitors

* newbg --color=red (or similar)

