fix: not treat form feed as line break (#443)

[tomoto]

This is the suggested fix for issue #443. Please see it for the exact description about what this fix is trying to address.

The issue is caused by splitting the code into lines using str.splitlines built-in function, which has a different set of line separators than the editors. (See https://docs.python.org/3/library/stdtypes.html#str.splitlines ) This fix is using our own splitlines function instead to make the line separation rule more consistent with the editors.

Now fortls can return the correct information regardless of the form feed characters in the code.

[tomoto]

@gnikit I see "Some checks were not successful" message. If there are anything I should do, please let me know. Thank you for your time!