[PATCH] Add completion styling

[Tom Tromey]

Eli> Also, do we want the default styling to be no-styling, or do we want
Eli> something else?

>> I would prefer to enable it by default.  It's easy to disable if one
>> prefers.

Eli> But I thought the code disabled it by default?  I did I misread?

The default is magenta, and it's enabled if $TERM is set properly.

+cli_style_option completion_style ("completion", ui_file_style::MAGENTA);

Tom