Make slacker client a lazy initialized value. Also removed meta-remote
call in defn-remote, which requires slacker client to be connected
while declaring functions.
deref delay in use-remote
updated doc for use-remote
update README
working on #17. Added periodical ping.
bump link version to fixed reconnect issue
added try-catch in ping scheduler function to keep it running.
removed debug info
slacker client won't connect to server at creation. this prevents
slackerc function being blocked forever. since we cannot set timeout
on derefing delay object, we need to allow generation of tcp client
without blocking, and set timeout at function call.
remove (future) for async callback, leave it to user.
setup travis-ci build
fixed travis build file
clean up resources on closing
update handle-response to return result info, and unpack in invoke
slacker. exception won't be thrown from SlackerClient. to fix
https://github.com/sunng87/slacker-cluster/issues/5
update async call API:

1. callback now accept two argument: [error result] (breaking change)
2. async functions returns custom type of Promise, will throw
exception on deref if error.
also update inspect to return call-result.
fixed #19. removed request map and add slacker.client.state/server-requests
fixed close-all-slackerc, now call close-slackerc on each opened client
minor refactoring on async callbacks
update async callback api, user-friendly-exception
fixed exception handling in async call. also cleanup on-message callback.