Add support for the custom feature API

[brychanrobot]

AutoDesk put out a preview API for custom features earlier this year. https://help.autodesk.com/view/fusion360/ENU/?guid=GUID-FA7EF128-1DE0-4115-89A3-795551E2DEF2. I know a few people have previously requested that this plugin be able to update after creation (#24, #23). It would certainly be more convenient than deleting and re-creating, especially if there is any geometry built onto the gear. With this new API that should be possible. I know that the API is still in preview, but it could be prototyped in a branch until the API moves out of preview.