[RFC][python] Add support for convenience functions implemented in Python

[Eli Zaretskii]

> From: Thiago Jung Bauermann <bauerman@br.ibm.com>
> Date: Mon, 02 Feb 2009 11:16:44 -0200
> 
> gdb/doc/
> 2008-02-02  Tom Tromey  <tromey@redhat.com>
> 
> 	* gdb.texinfo (Convenience Vars): Document convenience functions.
> 	(Functions In Python): New node.
> 	(Python API): Update.

Approved, with comments:

> +@value{GDBN}.  The @var{name} argument is the name of the function.
> +This must be a string.  The function is made visible to the user as a
> +convenience variable, of ``internal function'' type, whose name is the
> +same as @var{name}.

Suggest to rephrase as follows:

  The argument @var{name} is the name of the function, a string.  The
  function will be visible to the user as a convenience variable of
  type @code{internal function}, whose name is the same as the given
  @var{name}.

Thanks.