Doc: make python function/method descriptions look as in Python

[Sergio Durigan Junior]

Thanks for the work, Paul.

<Paul_Koning@Dell.com> writes:

> I found the descriptions of the Python methods/functions hard to read because they are not shown in Python syntax.   The attached patch fixes that.

Please, send future patches to gdb-patches@sourceware.org.  As for the
review, I think Eli is more capable in this are than me.