Normalize line endings

Follows steps at https://help.github.com/articles/dealing-with-line-endings
Adds .gitattributes so committed text files will have normalized line endings in the repository (LF rather than CRLF)
Updates current instances (9 files) to have LF rather than CRLF line endings
git diff --ignore-space-at-eol can be used to show that no other changes were made