[RFC 0/8] add terminal styling to gdb

[Tom Tromey <tom@tromey.com>]

This series is not ready to review, but I wanted some feedback on the
general approach before committing to writing documentation, test
cases, and comments.

I've wanted gdb to use colors on the terminal for a while now.  I've
actually tried implementing this a few different ways at different
times, the most successful approach so far being a colorizing frame
filter.

This series takes a more direct approach, namely integrating the code
into gdb.  The basic approach is to have gdb know how to emit ANSI
terminal escape codes to control the color and style (currently just
the intensity).  Then, cli-out is changed to style certain fields as
it emits them.  However, because some places do not use ui-out, some
ad hoc changes are also done.

This series styles function names, file names, and variable names.  It
also styles the gdb welcome message for fun.

I think my earlier patch to make the TUI understand ANSI terminal
escapes will make this patch work there.  (I have not tried this yet.)

Other things could be styled as well.  A few ideas I had:

* Style addresses specially
* Style strings specially
* Add styling to "print" and "ptype" (like, field names could be
  styled the way they are in other spots in this series)
* Go the other way and instead of styling the names of variables,
  style their values
* Style gdb-provided identifiers specially so they can be found
  more easily; here I mean something like the thread number or
  breakpoint number, which you have to read to type back to gdb
  sometimes
* Inferior-provided identifiers (PID or thread name) could be styled
  differently too
* ... your idea here, let me know

Tom