Add initial draft on repeatable transfers
Add support for repeatable isochronous transfers
Add repeatable control transfers
Merge branch 'master' into repeatable-transfers

Conflicts:
	System/USB/Base.hs
Exported the repeatable control transfers & Refactoring
Inline marshallCallbackRegistrationStatus
Fix a bug in setReadTransferSize when size == 0
Add repeatable control write transfers
Added default.nix and shell.nix
Removed note about the async impl. not working on GHC-7.8 from Changelog

Because we now have a nice work-around.
Added repeatable control transfers (that don't transfer data)
Added some basic documentation to System.USB.IO.Transfers
Replace the ControlAction function by the ControlSetup record
Only export System.USB.IO.Transfers when the event manager is available