[Shepherd] Use query string for searches

While running some searches in Shepherd I noticed that the URL gets really really
long, and seems to get cut off. Also there's a pattern of
   .../author/name1/author/name2/author/name3/
which seems really weird. Those are name-value pairs, they should be represented
as such.

Seems to me we should be using a query string here, not path segments. For simple
searches, maybe returning a path segment could be pretty, but for more complicated
ones it doesn't seem to work very well.

~fantasai