121 add line ending options 1

[daira]

fixes #121

[techtonik]

I am not sure that it is a job of modernize tool to convert linefeeds. This is more like a job for code formatters like go fmt. And even if modernize has this option, I expect it to run and rewrite files even if I didn't run any fixers. Well, actually, these formatting options look like fixers themselves.

[graingert]

@daira I think this should be done on fissix, also closing in favour of #131

changing lines wholesale can be done with https://github.com/pre-commit/pre-commit-hooks#mixed-line-ending