Enforce normalization of line endings

[tsaglam]

We should enforce line ending normalization though a .gitattributes file. Each of our repositories needs such a file:

# Set the default behavior, in case people don't have core.autocrlf set.
* text=auto

Also, we then should once normalize all line endings with git add --renormalize .. However, this might produce many changes to commit, the timing of this PR should thus selected carefully to avoid conflicts with other branches and forks.

TL;DR:

• [x] Add .gitattributes files to each repo
• [x] Normalize all files in each repo