Added a .gitattributes file to set the line ending behavior when checkin...

...g out/committing

I think I've covered all important file extensions

I did find some other's which I didn't cover explicitly:
1 x .editorconfig
1 x .gitignore
1 x .gitattributes (the new file itself)

And some special fiiles under Test somewhere:
2 x *.swf
1 x *.text
1 x *.htc

Not sure whether *.pem couldn't be moved to the "text" ones above.

Under binary there could be many more file extensions but only these I have found within the current repo.

Kudos to @shama for pointing this out in [his comment](https://github.com/cakephp/docs/pull/842#issuecomment-27058191).