Improve on missing newline in a file by adding line number

[bwbroersma]

Although #21 was fixed in #35 (by these 5 lines in 4dc8b2b), the current error does not list the line number, nor indicate that it's about the last line of the file:

[
  {
    'code': 'no_line_separators',
    'message': 'Every line must end with either a carriage return and line feed characters or just a line feed character',
    'line': None
  }
]

Either:

1. the line number must be specified; and/or
2. the text message should be made explicit it's about the last line.

So the problem in the code is here:

sectxt/sectxt/__init__.py

Lines 92 to 93 in 79bb386

	self._line_no = None
	self.validate_contents()

It set's the _line_no to None, and then in validate_contents the check is done:

sectxt/sectxt/__init__.py

Lines 284 to 290 in 79bb386

	if self.lines[-1]["type"] != "empty":
	self._add_error(
	"no_line_separators",
	"Every line must end with either a carriage "
	"return and line feed characters or just a line "
	"feed character",
	)

In the _add_error the _line_no is used:

sectxt/sectxt/__init__.py

Lines 95 to 101 in 79bb386

	def _add_error(
	self,
	code: str,
	message: str,
	) -> None:
	err_dict: ErrorDict = {"code": code, "message": message, "line": self._line_no}
	self._errors.append(err_dict)

I would propose doing both:

1. Add explicit_line_no=None to the _add_error definition, plus self._line_no if explicit_line_no = None else explicit_line_no and a self.lines[-1]._line_no to the _add_error call in the 'empty content after \r?\n' check in validate_contents.
2. Change the text to 'Every line, including the last one, must end with either a carriage return and line feed characters or just a line feed character'

[DigitalTrustCenter]

With the new release the line is added with the missing newline error and the error message has been clarified.