Rex::Text::Ui::Table.new[find_by_colnames]

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
```

lib/rex/ui/text/table.rb

@@ -212,6 +212,24 @@ class Table
 		rows << '__hr__'
 	end
 
+        #   
+        # Returns new sub-table with headers and rows maching column names submitted
+        #   
+        def [](*colnames)
+                tbl = self.class.new('Indent' => self.indent,'Header' => self.header,'Columns' => colnames)
+                idx = []
+                colnames.each do |colname|
+                        idx << self.columns.index(colname)
+                end 
+                self.rows.each do |oldrow|
+                        newrow = []
+                        idx.map {|i| newrow << oldrow[i]}
+                        tbl << newrow
+                end 
+                return tbl 
+        end 
+
+
 	alias p print
 
 	attr_accessor :header, :headeri # :nodoc: