[DOC] Refine packed_data.rdoc

* Escape unexpected links
* Remove unnecessary path name from in-file reference

Author: nobu

doc/language/packed_data.rdoc

@@ -151,15 +151,15 @@ Any directive may be followed by either of these modifiers:
     [65, 66].pack('C*') # => "AB"
     'AB'.unpack('C*')   # => [65, 66]
 
-- Integer +count+ - The directive is to be applied +count+ times:
+- \Integer +count+ - The directive is to be applied +count+ times:
 
     [65, 66].pack('C2') # => "AB"
     [65, 66].pack('C3') # Raises ArgumentError.
     'AB'.unpack('C2')   # => [65, 66]
     'AB'.unpack('C3')   # => [65, 66, nil]
 
   Note: Directives in <tt>%w[A a Z m]</tt> use +count+ differently;
-  see {String Directives}[rdoc-ref:language/packed_data.rdoc@String+Directives].
+  see {\String Directives}[rdoc-ref:@String+Directives].
 
 If elements don't fit the provided directive, only least significant bits are encoded: