Automatically detect the proper line ending

[Pacu2]

Text files created on DOS/Windows machines have different line endings than files created on Unix/Linux. DOS uses carriage return and line feed ("\r\n") as a line ending, which Unix uses just line feed ("\n").
Source: http://www.cs.toronto.edu/~krueger/csc209h/tut/line-endings.html#:~:text=Text%20files%20created%20on%20DOS,(%22%5Cn%22).

Darker should not modify the line ending as it results in false-positives.

E.g.

1. Create a file on Windows
2. All line endings are equal \r\n
3. Modify the file with Darker
4. Every line gets modified, \r\n line ending is changed to \n
5. In git-diff it looks like every single line was modified

Black on the other hand tries to check for the proper line ending
newline = "\r\n" if b"\r\n" == lines[0][-2:] else "\n"

[Pacu2]

@akaihola I think I can handle this at sometime during the week

[akaihola]

@Pacu2, I thought about this a bit and figured that the file encoding should also be handled correctly. Please see #117.