Introducing DocumentFactory

This new release make instantiating documents easier.

There are some breaking changes as described below:

# previously...
$document = new Document('file.pdf');
$document->feedFromPath('/path/to/file');

# ... now:
$document = DocumentFactory::makeFromPath('file.pdf', '/path/to/file');

# previously...
$document = new Document('file.pdf');
$document->feedFromStream(new LazyOpenStream('path/to/file', 'r'));

# ... now:
$document = DocumentFactory::makeFromStream('file.pdf', new LazyOpenStream('path/to/file', 'r'));