Fix defined for static compile.

See https://bugs.php.net/bug.php?id=63086
Merge branch 'pull-request/2'

Apply patch from @reeze that declares extern for yaml_module_entry needed to
statically compile module with php.

Closes #63086
Add maintainer/developer tools.

- created dev-tools directory
- moved existing maintainer-clean and test runner scripts to dev-tools
- moved README.packaging to dev-tools
- new pull-request script for handling github pulls