core libs for s3, ec2, ssh.

build upon the core is remote repl and cluster capabilities.

in a couple cases, we use an erlang convention of the ! syntax representing "reomote" (on another process) execution.
the first argument to ! in erlang is the pid, wheras in our api, it is an open ssh session or socket.
there is no ! operator or fn, we just use the ! suffix convention to communicate remote execution.

remote shell execution.
(sh! session "tar -xzf repl.tar.gz")

remote repl evaluation.
eval! 
(eval! socket (execute (workflow some-cascading-workflow)))

TODO: add examples for usages.

TODO:
the persistent shell session using jsch ChannelShell is shaky at best, although exec works fine.
eval! may be simpler if we could use LineNumberingPushbackReader see comment in remote_repl.clj
stuff to poll and pull info from hadoop tracker url into repl

== Usage: crane.ec2

  (ns crane.demo
    (:use crane.ec2))

  (def my-ec2
    (ec2 {:key "somekey" :secretkey "somesecret/key"}))
  
  (def basic-fedora "ami-3c47a355")
  
  (run-instances my-ec2 
    {:instance-type (instance-types :m1.small)
     :image basic-fedora
     :instances 1
     :key-name "gsg-keypair"
     :group "default"})