ed3b1cecd4
Add :[] to ...Ui::Table allowing user to pass multiple colnames.
Returns a new table with only those columns and their rows.
Useful when using Rex to filter output, prep CSV, etc.
Testing:
```
t = Rex::Ui::Text::Table.new('Columns' => ['a','b','c'])
t << ['x','y','z']
t << ['p','q','r']
t['a','c']
=> a c
- -
p r
x z
```