This release brings a major overhaul of postcode handling and the PHP frontend code.
Postcodes now reside in their own table location_postcode which can be updated at any time. Postcodes for places are no longer part of the standard address but are guessed with using a dedicated algorithm. On the search side, post codes can now be ignored in the query, improving results in areas where postcode coverage in OSM is bad. For more details read this blog post.
The PHP frontend code that parses incoming queries and looks up and formats the results has been thoroughly refactored into a set of classes with much smaller functions. All code is now documented and the API tests have resulted in almost 100% code coverage. As part of these changes there have been a lot of small tweaks to the algorithm that interprets the incoming queries to exclude more unlikely interpretations.
For a more complete list of changes, see the ChangeLog file.
If you want to update from 3.0.x, there is a database migration path described in the migration guide. However, to fully profit from the postcode changes a full database reimport is strongly recommended. Updating from older releases is only possible with a database reimport.