Fix autoloading when installed as a dependency

Previously, when the project was installed as a dependency through composer the `generate` script could not find the autoloader.

This commit resolves that by checking whether the autoloader exists in the current directory (i.e. not as a dependency) or whether the autoloader exists two directories up (i.e. as a dependency). If neither of these paths exist the script will gracefully fail.
Merge pull request #2 from rawebone/fix-install-as-dependency-autoloading

Fix autoloading when installed as a dependency