Provide a standalone command line tool

This pull request provides all-in-one JAR as a command line tool.

We can run a Groovy script by `java -jar groovy-ssh-x.y.z-all.jar` as follows:

```
% java -jar groovy-ssh-0.1.4-all.jar -i -e 'ssh.run { session(host: "localhost", user: "example", identity: new File("~/.ssh/id_rsa")) { execute("uname -a") } }'
21:19:01.470 [main] INFO  o.h.g.s.i.c.DefaultConnectionManager - Established a session to Remote localhost [localhost:22] via localhost:22
21:19:01.561 [main] INFO  o.h.g.s.i.s.DefaultSessionHandler - Execute a command (uname -a)
21:19:01.600 [main] INFO  o.h.g.s.i.o.DefaultOperations - Channel #0 has been opened
21:19:01.653 [Connect thread localhost session] INFO  o.h.g.s.i.o.DefaultOperations - Darwin example.local 14.0.0 Darwin Kernel Version 14.0.0: Fri Sep 19 00:26:44 PDT 2014; root:xnu-2782.1.97~2/RELEASE_X86_64 x86_64
21:19:01.703 [main] INFO  o.h.g.s.i.o.DefaultOperations - Channel #0 has been closed with exit status 0
```