Markdown.pl: tidy up some regex options

The %g_escape_table hash gets initialized in a BEGIN block and then
remains constant for the life of Markdown.pl.

Add the "o" (compile pattern once) option to all the patterns that
it appears in to perhaps squeeze out just a tiny little bit of extra
performance if possible.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>

Markdown.pl

@@ -1835,7 +1835,7 @@ sub _EscapeSpecialChars {
 	    # corresponding block id value; this is likely
 	    # overkill, but it should prevent us from colliding
 	    # with the escape values by accident.
-	    $cur_token->[1] =~ s!([*_~])!$g_escape_table{$1}!g;
+	    $cur_token->[1] =~ s!([*_~])!$g_escape_table{$1}!go;
 	    $text .= $cur_token->[1];
 	} else {
 	    my $t = $cur_token->[1];
@@ -1989,7 +1989,7 @@ sub _MakeATag {
     $text = _DoItalicsAndBoldAndStrike($text);
     # We've got to encode any of these remaining to avoid
     # conflicting with other italics, bold and strike through and links.
-    $text =~ s!([]*_~[])!$g_escape_table{$1}!g;
+    $text =~ s!([]*_~[])!$g_escape_table{$1}!go;
     $result .= " title=\"" . _EncodeAttText($title) . "\"" if $title ne "";
     return $result . $g_escape_table{'>'} .
 	$text . $g_escape_table{'<'}."/a".$g_escape_table{'>'};
@@ -2385,7 +2385,7 @@ sub _EncodeAttText {
     $text = escapeXML(_strip($text));
     # We've got to encode these to avoid conflicting
     # with italics, bold and strike through.
-    $text =~ s!([*_~:])!$g_escape_table{$1}!g;
+    $text =~ s!([*_~:])!$g_escape_table{$1}!go;
     return $text;
 }
 
@@ -3125,7 +3125,7 @@ sub _EncodeCode {
     s! >  !&gt;!gx;
 
     # Now, escape characters that are magic in Markdown:
-    s!([*_~{}\[\]\\])!$g_escape_table{$1}!g;
+    s!([*_~{}\[\]\\])!$g_escape_table{$1}!go;
 
     return $_;
 }
@@ -3140,7 +3140,7 @@ sub _DoItalicsAndBoldAndStrike {
 	    {<em>$1</em>}gsx;
 	# We've got to encode any of these remaining to
 	# avoid conflicting with other italics and bold.
-	$text =~ s!([*])!$g_escape_table{$1}!g;
+	$text =~ s!([*])!$g_escape_table{$1}!go;
 	$text;
     };
     my $doital2 = sub {
@@ -3149,7 +3149,7 @@ sub _DoItalicsAndBoldAndStrike {
 	    {<em>$1</em>}gsx;
 	# We've got to encode any of these remaining to
 	# avoid conflicting with other italics and bold.
-	$text =~ s!([_])!$g_escape_table{$1}!g;
+	$text =~ s!([_])!$g_escape_table{$1}!go;
 	$text;
     };
 
@@ -4074,7 +4074,7 @@ sub _EncodeBackslashEscapes {
     local $_ = shift;
 
     s!\\\\!$g_escape_table{'\\'}!go; # Must process escaped backslashes first.
-    s{\\([`*_~{}\[\]()>#+\-.!`])}{$g_escape_table{$1}}g;
+    s{\\([`*_~{}\[\]()>#+\-.!`])}{$g_escape_table{$1}}go;
 
     return $_;
 }