Strip trailing whitespace and fix line/file ending

[AlekSi]

There are a lot of files with lines with trailing spaces or without \n at EOF. That makes merging harder than it could be.

I propose adding an Editor Config to remove them.

(One problem is the expected output of tests that should be adjusted.)

[AlekSi]

Not sure why it was moved from #138 to this discussion if no one is discussing anything…