v0.2-alpha

• Keyframes can now be mirrored horizontally and vertically
• Animations can now be duplicated
• Deleting a frame will now warn you if there are any keyframes still using that frame (if user confirms, any keyframes referring to that frame will also be deleted)
• Added new document version system, so documents saved in old versions of the tool can be migrated to new versions (documents saved in a newer version of the tool will fail to load with an error message)
• Various document format changes & refactors