Add .gitattributes file

This way we can exclude files in production by installing with the --prefer-dist flag.

Author: vinkla

.gitattributes

@@ -0,0 +1,9 @@
+* text=auto
+
+/example export-ignore
+/test export-ignore
+/.gitattributes export-ignore
+/.gitignore export-ignore
+/.travis.yml export-ignore
+/phpunit.xml.dist export-ignore
+/README.md export-ignore