Improvements on the script commands sscanf, axtoi. Added strtol.

- Added script command strtol (conforming to the ISO C90 function)
- Modified script command axtoi to internally use strtol instead of an
  unnecessary own implementation.
- Fixed sscanf behavior to conform to the C specifications in case the
  input string is empty. It now correctly returns -1, or 0 if the format
  string is also empty. Fixes bugreport:8009, thanks to AnnieRuru -
  http://hercules.ws/board/tracker/issue-8009-sscanf-should-return-1-if-the-string-field-is-an-empty-string/

Signed-off-by: Haru <haru@dotalux.com>