Only substitute characters from auto generated fields in _PostPathFormatter
This fixes issues of path problem on Windows such as #304, #529, etc.
Also made the following changes:
1. Changes substitution of colon to full-width colon (U+FF1A) instead of MODIFIER LETTER COLON (U+A789) to be consistent with others (we use full-width backslash, pipe, etc. already).
2. Also replaces `\r` on Windows with space, just like `\n`.
