tweaks: highlight keystrokes in the documentation more consistently

doc/nano.1

@@ -281,8 +281,8 @@ Set the operating directory.  This makes \fBnano\fP set up something
 similar to a chroot.
 .TP
 .BR \-p ", " \-\-preserve
-Preserve the XON and XOFF sequences (^Q and ^S) so they will be caught
-by the terminal.
+Preserve the XON and XOFF sequences (\fB^Q\fR and \fB^S\fR) so they
+will be caught by the terminal.
 .TP
 .BR \-r\ \fInumber ", " \-\-fill= \fInumber
 Set the target width for justifying and automatic hard-wrapping at this

doc/nano.texi

@@ -1249,7 +1249,7 @@ Throws away the current line (or the marked region).
 Deletes from the cursor position to the beginning of the preceding word.
 (This function is bound by default to <Shift+Ctrl+Delete>.  If your terminal
 produces @code{^H} for <Ctrl+Backspace>, you can make <Ctrl+Backspace> delete
-the word to the left of the cursor by rebinding ^H to this function.)
+the word to the left of the cursor by rebinding @kbd{^H} to this function.)
 
 @item chopwordright
 Deletes from the cursor position to the beginning of the next word.

doc/nanorc.5

@@ -179,7 +179,7 @@ System, and on the console when gpm is running.  Text can still be
 selected through dragging by holding down the Shift key.
 .TP
 .B set multibuffer
-When reading in a file with ^R, insert it into a new buffer by default.
+When reading in a file with \fB^R\fR, insert it into a new buffer by default.
 .TP
 .B set noconvert
 Don't convert files from DOS/Mac format.
@@ -213,7 +213,7 @@ Save the cursor position of files between editing sessions.
 The cursor position is remembered for the 200 most-recently edited files.
 .TP
 .B set preserve
-Preserve the XON and XOFF keys (^Q and ^S).
+Preserve the XON and XOFF keys (\fB^Q\fR and \fB^S\fR).
 .TP
 .BI "set punct """ characters """
 Set the characters treated as closing punctuation when justifying
@@ -571,7 +571,7 @@ Throws away the current line (or the marked region).
 Deletes from the cursor position to the beginning of the preceding word.
 (This function is bound by default to <Shift+Ctrl+Delete>.  If your terminal
 produces \fB^H\fR for <Ctrl+Backspace>, you can make <Ctrl+Backspace> delete
-the word to the left of the cursor by rebinding ^H to this function.)
+the word to the left of the cursor by rebinding \fB^H\fR to this function.)
 .TP
 .B chopwordright
 Deletes from the cursor position to the beginning of the next word.