Add command "ssh"

Usage:

    $ pecrant ssh
Merge pull request #2 from gongo/add-ssh

Add command "ssh"
Alternative of `pecrant cd`
Merge pull request #3 from gongo/alternative_pecrant_cd

Alternative of `pecrant cd`
Add box commands
Revise the main help
Add `pecrant dir` instead of `pecrant list`

refs GH-3

In order to use the pipe, leave "pecrant list" command to output all columns.
Merge pull request #5 from gongo/pecrant-dir

Add `pecrant dir` instead of `pecrant list`
Support directory that contains space
Merge pull request #6 from gongo/contains-space

Support directory that contains space
Merge remote-tracking branch 'yungsang/box'
Correspond to situation that requires a TTY
Fix README.md about `pecrant box`
Merge pull request #7 from gongo/required_tty_on_box-remove

Required tty on box remove
Forgot to add box into help
Merge pull request #8 from YungSang/box

Forgot to add box into help
Add ssh & cd for iTerm2
Refactoring based on https://github.com/gongo/pecrant/pull/7