Normalize repo to LF (Unix) line-endings, enforce (#654)

- A top-level .gitattributes sets the attribute 'text=auto' for all
  files in the repo, enabling line-ending normalization
- A `git add --renormalize` run converted any existing CRLF files
  to the canonical LF format.
- 'text=auto' permits Git on Windows to convert files to CRLF
  automatically on checkout, for convenience. Any commits
  added will be converted back to the repo format for checkin.

.gitattributes

@@ -0,0 +1,2 @@
+* text=auto
+