[shell] Add `cc` alias for copying to clipboard

See also:

 * http://manpages.ubuntu.com/manpages/natty/man1/xclip.1.html
 * https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man1/pbcopy.1.html
[shell] Use `osx` instead of `mac`
[lib] Add ability to generate SSH key

Ref: https://help.github.com/articles/generating-ssh-keys