path: replace "magic" numbers by readable constants

PR-URL: nodejs#18654
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Kyle Farnung <kfarnung@microsoft.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

lib/internal/constants.js

@@ -0,0 +1,16 @@
+'use strict';
+
+module.exports = {
+  // Alphabet chars.
+  CHAR_UPPERCASE_A: 65, /*A*/
+  CHAR_LOWERCASE_A: 97, /*a*/
+  CHAR_UPPERCASE_Z: 90, /*Z*/
+  CHAR_LOWERCASE_Z: 122, /*z*/
+
+  // Non-alphabetic chars.
+  CHAR_DOT: 46, /*.*/
+  CHAR_FORWARD_SLASH: 47, /*/*/
+  CHAR_BACKWARD_SLASH: 92, /*\*/
+  CHAR_COLON: 58, /*:*/
+  CHAR_QUESTION_MARK: 63, /*?*/
+};