* 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.

 * Splitting across multiple monitors

 * newbg --color=red (or similar)

 * refactoring: consider Wallpaper as object
  - std. routines to get brightness, pick, set

 * profiling
