Normalize line endings to LF

[peppy]

We probably want to do this. Unfortunately it's going to rewrite a lot of files, but kind of unavoidable.

• Switches to applying line endings on checkout.
• Uses CRLF for c# files for now, although this if likely not needed if users set autocrlf correctly.

Should have no effect on existing PRs (have already tested a merge).

References: https://help.github.com/articles/dealing-with-line-endings/ and boogie-org/boogie#15