[ANN] Release 3.5

[Andrus Adamchik]

Agrest 3.5 was released yesterday. The main change in this release is a split of Cayenne runtime away from Agrest core. So now we have two separate modules - "agrest-engine" and "agrest-cayenne", and conceivably one can build an alternative backend (which can be greatly assisted by @Ag* annotations already present in the core). Still a few things that require cleanup. E.g. the core still depends on Cayenne as a library (not as runtime) for expression parsing, etc. Also perhaps a more prominent SPI is needed for those future pluggable backends.

Check the upgrade notes for (fairly minor) changes in how bootstrap is done. Also Bootique 2.0 already integrates 3.5.

Release notes:

* #433 "agrest-cayenne" : isolate a pluggable Cayenne backend for Agrest
* #443 Null-safe AgRequestBuilder

Andrus