Merge pull request #410 from anacrolix/webseeds

Merge pull request #410 from anacrolix/webseeds

* Rename Peer to PeerInfo, and unexport PeerInfos

* Break peer out from PeerConn

* Abstract out segments mapping and use it in mmap storage

* Got file storage working with segment index

* Fix race in webtorrent.TrackerClient.Run

* storage file implementation: Error on short writes

* Remove debug logging from storage file implementation

* cmd/torrent-verify: Fix piece hash output

* Support disabling webtorrent

* Further progress on webseeding

* Handle webseed Client events

* Rename fastestConn->fastestPeer

* Add webseeds from magnet links

* Remove events from webseed

Manage this stuff inside the webseed peer instead.

* Make use of magnet source fields and expose Torrent.MergeSpec

* Add option to disable webseeds

* Fix webseeds when info isn't available immediately

* Handle webseed request errors

* Tidy up the interface changes