PCBC-997: Do not export development files (#172)

Exclude C++ files, tests and development scripts, so that Packagist will
not install them to the application ./vendor directory.

Author: avsej

.gitattributes

@@ -0,0 +1,6 @@
+/*.yaml export-ignore
+/.* export-ignore
+/bin export-ignore
+/compile_commands.json export-ignore
+/src export-ignore
+/tests export-ignore