Move the styling for the HTML version of \mailheader into the CSS file.

In both the HTML and typeset versions of the documentation, add a colon
after the name of a mail header so that it is more easily distinguished
from other text.

Doc/html/style.css

@@ -72,6 +72,7 @@ var                     { font-family: times, serif;
                           font-size: 85%; }
 
 .email                  { font-family: avantgarde, sans-serif; }
+.mailheader             { font-family: avantgarde, sans-serif; }
 .mimetype               { font-family: avantgarde, sans-serif; }
 .newsgroup              { font-family: avantgarde, sans-serif; }
 .url                    { font-family: avantgarde, sans-serif; }

Doc/perl/python.perl

@@ -213,7 +213,7 @@ sub do_cmd_longprogramopt{
 sub do_cmd_email{
     return use_wrappers(@_[0], '<span class="email">', '</span>'); }
 sub do_cmd_mailheader{
-    return use_wrappers(@_[0], '<tt class="mimeheader">', '</tt>'); }
+    return use_wrappers(@_[0], '<span class="mailheader">', ':</span>'); }
 sub do_cmd_mimetype{
     return use_wrappers(@_[0], '<span class="mimetype">', '</span>'); }
 sub do_cmd_var{

Doc/texinputs/python.sty

@@ -833,7 +833,7 @@
 \newcommand{\ctype}[1]{\texttt{#1}}     % C struct or typedef name
 \newcommand{\cdata}[1]{\texttt{#1}}     % C variable, typically global
 
-\newcommand{\mailheader}[1]{\texttt{#1}}
+\newcommand{\mailheader}[1]{{\small\textsf{#1:}}}
 \newcommand{\mimetype}[1]{{\small\textsf{#1}}}
 % The \! is a "negative thin space" in math mode.
 \newcommand{\regexp}[1]{%