Fix to work w/ composer and PSR-0 autoloaders

Class / namespace mis-match in composer.json prevents standard autoloaders from finding the BulletProof class.

Moved source code into proper subdirectory, adjusted composer.json to match.

If your future idea is a set of "BulletProof" classes, then you should make the overall namespace be "BulletProof" and the class name "ImageUploader", so that people will do "new \BulletProof\ImageUploader();". That would require several further renames to directories and files though.