Print compact tables with no decorations

Hello,
 I wanted to be able to use cli-table to print columned data in a ultra-compact mode with no decorations whatsoever.

To accomplish this, I wrote some patches adding the following capabilities to cli-table:

1. have a vertical cell separator different from the right border
2. completely omit vertical decoration lines if empty, instead of printing '\n'

I've added some test to prevent the most obvious breackage.

Let me know if there's any change you'd like to see applied.

Thanks!