If require-starting-space is true, *and* either:
- new-lines: disbale, or
- newlines: type: dos
is specified, a line with `#\r` or `#\r\n` should
not raise a false positive.
This commit also uses a Set for O(1) membership testing
and uses the correct escape sequence for the nul byte.
Closes: Issue #171.
765cce0d3e