Code review

I have reviewed the module. There are a lot of different bits and pieces. The major points are:

1. The relationship between node, field, settings and output is very convoluted to me. This should be refactored.
2. Methods for http and database access needs refactoring. This includes method separation and error handling.
3. The Drupal API should be used to extract information. `entity_metadata_wrapper()` over array extraction. Less/no `db_query()`.
4. Elements and methods should be prefixed with `ding_place2book`.