Before anyone freaks out, all these changes are under-the-hood, meaning that you probably won't even notice them at all.
The biggest difference is raising the minSdkVersion from 9 to 14. Recently android bumped this number interally as there are basically no devices running lower than 14 anymore. Sorry but you are just wasting your time if you are trying to support anything lower than 14 now.
The next biggest change is updating the project to the new AndroidX libraries, which changes some imports and nothing else really.
The third biggest change is fixing a few bugs in the code that cause values to be drawn even if there are none, which results in your app crashing. Surprisingly, these checks already existed in a few of the newer chart types, but most lacked this simple check.
Other than those three changes, nothing else is functionally different. Well, saving to gallery works on all charts in the example app now, and you can quickly see the code for each example in the menus.
The only real potential "breaking" change is that charts are now saved as PNGs by default instead of JPGs if you go the route of not specifying as a JPG. You may want to double check your file sizes as PNGs can be larger than low quality JPGs.
I still have more plans for simplifying the API and fixing other issues with the project, for the small few that closely pay attention to individual commits: there's going to be more soon.
