I'm currently working on an app to ease the versioning of C3 projects. The repo is here github.com/JeyDotC/c3-git
The basic worflow is this:
1. Save the project to a cloud service
2. Make sure it is synched to a local folder.
3. Create an empty folder and run this command: c3git init /path/to/synched/project.c3p
That will create a folder with the project contents and an appropriate gitignore.
4. Make your changes in C3 editor and wait for file syncing.
5. Call this command: c3git commit -m "your message"
That will extract the changes from the project and commit them.
6. Follow your regular git process.
7. To mount things back from folder to file, call: c3git mount
Tha will create a backup of the project file, zip the folder and replace it.
8. Wait for sync, close the project and open it again.