Old client to future

[bluejekyll]

Rearchitected the original Client into SyncClient and SecureSyncClient. This is a breaking change.

@zsck if you have a minute, would you mind looking at this and let me know if these changes are too aggressive? It should be a relatively straightforward upgrade. You're currently the only person I know is relying on this.

[coveralls]

Coverage increased (+3.6%) to 89.89% when pulling 39c8813 on old_client_to_future into 01c0153 on master.

[bluejekyll]

coverage, 90% badge, woohoo!

[coveralls]

Coverage increased (+3.6%) to 89.89% when pulling aa0216a on old_client_to_future into aeb484a on master.

[mathstuf]

Note that this means that users which are required to be Send + Sync must now create a resolver on each use rather than being able to create their Client just once. See #227.

[bluejekyll]

All client handles are cloneable, not sync. Have you tried using clone to facilitate your needs?