Abstracting out shard mappings

[Mark Miller]

What do you think about adding further ways to control how the shard 
parameter works with distributed search? Perhaps something like a 
ShardMapper. It would allow things like setting up the ips in config and 
then using shard parameters like shards=1-100 shards=1-10,15-20 
shards=1,4,5 etc.

Trying to think of something to handle how unwieldy the GET urls can get 
at large scale...