Alpha 4.0 release

Alpha 4.0 is here! I decided to make this a major release rather than calling it 3.1 because adding the ability to save felt like a significant enough change, especially combined with all the new content. Alpha 4.1 is probably coming in late December, and it will be mostly bugfixes and art updates (there are a number of placeholder images I left in so that I could rush out this release before the end of the month).