Add fix for line length detection under Windows

Hey there. The line length rule is currently overly harsh under Windows, where it rejects lines of 80 characters due to the `\r` in `\r\n` being counted as an 81st character.

This patch provides a test case illustrating the problem as well as a simple fix which also plays nice with the line ending rule.

Caveat: Didn’t test it under Windows myself, only ran the test suite.