Show version when -v flag is passed

Prior to this commit, the OptionParser defaults for show_version were used
which resulted in:

    $ veewee-to-packer -v
    veewee-to-packer: version unknown
Replace <Backspace> with <bs> in boot commands

Packer passes `<Backspace>` right through, which isn't what the user intended.
`<bs>` is handled correctly.
Merge pull request #17 from Sharpie/misc-fixes

Correctly translate <Backspace> and display version number