I didn't push 3.4.0.0 to github because I was on a flight when I pushed it to steam, so you're getting 2 updates in one.
3.4.0.0 finally added support for 1.4 and did a load of code cleanup.
3.5.0.0 extends that to 1.5 (assuming nothing changes between current unstable and full release of 1.5) and improves the amount of detail provided when loading into a savegame.