[FEATURE] Keep development-only files out of the Composer packages (#269)

This will reduce download size and improve download speed when this
package is used.

Author: oliverklee

.gitattributes

@@ -0,0 +1,7 @@
+/.Build/ export-ignore
+/.editorconfig export-ignore
+/.gitattributes export-ignore
+/.github/ export-ignore
+/.gitignore export-ignore
+/Build/ export-ignore
+/Tests/ export-ignore