tweaks: properly escape "\" in a man page and "@" in a texi document

Also make the involved sentences more precise.

doc/nano.texi

@@ -1075,12 +1075,12 @@ The format of @code{key} should be one of:
 
 @itemize @w{}
 @item
-@code{^}@  followed by a Latin letter, one of several ASCII characters
-(@, ], \, ^, or _), or the word "Space".
+@code{^}@  followed by a Latin letter, by one of several ASCII characters
+(@@, ], \, ^, or _), or by the word "Space".
 Example: @code{^C}.
 
 @item
-@code{M-}@  followed by any ASCII character except [, or the word "Space".
+@code{M-}@  followed by any ASCII character except [, or by the word "Space".
 Example: @code{M-C}.
 
 @item

doc/nanorc.5

@@ -427,17 +427,17 @@ The format of \fIkey\fP should be one of:
 .RS 3
 .TP 3
 .B ^
-followed by a Latin letter, one of several ASCII characters
-(@, ], \, ^, or _), or the word "Space".
-Example: ^C
+followed by a Latin letter, by one of several ASCII characters
+(@, ], \\, ^, or _), or by the word "Space".
+Example: ^C.
 .TP
 .B M-
-followed by any ASCII character except [, or the word "Space".
-Example: M-C
+followed by any ASCII character except [, or by the word "Space".
+Example: M-C.
 .TP
 .B F
 followed by a numeric value from 1 to 16.
-Example: F10
+Example: F10.
 .TP
 the word "Ins" or the word "Del".
 .RE