replace multiple Send's with single
update example
added AgentView
export send
factored out sender/receiver info
updated examples/abt.hs
abstract over messages in example
change import to Free.Class
abstract send/receive interface
use SendRecv for ABT
add SendRecv to exposed modules
update example
rename MsgNoGood to MsgBacktrack
added Control.Agent.Free.Interfaces
STM environment
abstract over MonadReader and MonadIO
fix Map.alter bug
fix stop bug
fix constraint transform
use SendRecv STM interpreter in example