added GetHostCount function
modified request object to force connections to close
changed proxy to nil
Merge branch 'semaphore' into dev
Modifed WorkerIdleTTL logic

Before, WorkerIdleTTL would cause a host goroutine to be killed
when no new links were inserted into the goroutine in WorkerIdleTTL time.
The new behavior is, WorkerIdleTTL will cause a host goroutine to
be killed when the host goroutine has not crawled a page in
WorkerIdleTTL. This allows a host goroutine to build a large
queue of links and have time to crawl them all, rather than being cut
short by the old behavior.
added support for resizing the concurrency semaphore
added download time logging
Merge branch 'resizeableSemaphore' into dev

Conflicts:
	fetch.go
fixed SetConcurrency so that it updates the concurrency member of fetcher
modified semaphore behavior to reduce duration inside semaphore
removed resizeable semaphore, causing downloads to stop
Merge branch 'dev'