Declare our public API #248
Description
We should formally declare what's part of our public API, so that users are aware of what will be kept stable and what's subject to change without warning or tick-tock.
Take into account:
- Public headers and what it means if they're in a
detailsfolder - CMake functions from
gz-cmake - CLI arguments
- Binary symbols
- Protobuf namespaces
A good reference is REP-2004 and the quality declarations of existing packages, like rclcpp.
We could place this documentation in releases together with versioning and deprecation strategies.