Ignore inessential files for git export

Author: jakzal

.gitattributes

@@ -0,0 +1,16 @@
+/.gitattributes export-ignore
+/.github export-ignore
+/.gitignore export-ignore
+/.php_cs export-ignore
+/.travis.yml export-ignore
+/CODE_OF_CONDUCT.md export-ignore
+/CONTRIBUTING.md export-ignore
+/Makefile export-ignore
+/box.json.dist export-ignore
+/composer.json export-ignore
+/depfile.yml export-ignore
+/infection.json.dist export-ignore
+/manifest.xml.in export-ignore
+/phpunit.xml.dist export-ignore
+/tests export-ignore
+/tools export-ignore