BUGFIX: char() is processor dependent, use achar()

- achar(i) ensures ascii charater at i in collating sequence
- switched '\' to achar(92) because Emacs was thinking '\'
  was escaping the second quotation mark, but in fortran
  '' inserts a literal quotation if single quotations are used
  as string delimiters. I realize that this is an Emacs bug,
  not a json-fortran bug, but it was making me crazy

All test with the Intel compiler still pass