Memory usage is very large

When I use this tool to query a lot of urls，urls will put the result to groutines，finally i find
resp, err := reqPool.PooledClient.Do(req) will create a a lot of groutines，and memory is fastly Growing。

[phayes]

It looks like it's leaking goroutines:

goroutine profile: total 12101
8340 @ 0x432df0 0x406cfb 0x406cd1 0x406ab5 0x935303 0xa34f3e 0xa34f22 0x460901
#	0x935302	github.com/ewohltman/pool.(*PClient).DoPool+0x132	/src/vendor/github.com/ewohltman/pool/pool.go:92
#	0xa34f3d	github.com/ewohltman/pool.(*PClient).Do+0x28d		/src/vendor/github.com/ewohltman/pool/pool.go:79

3576 @ 0x432df0 0x406cfb 0x406cd1 0x406ab5 0x935303 0xa341da 0xa341be 0x460901
#	0x935302	github.com/ewohltman/pool.(*PClient).DoPool+0x132	/src/vendor/github.com/ewohltman/pool/pool.go:92
#	0xa341d9	github.com/ewohltman/pool.(*PClient).Do+0x679		/src/vendor/github.com/ewohltman/pool/pool.go:79

[phayes]

It actually could be that it's not handling backpressure at all, and just spinning up goroutines until it OOMs.