The 1.0 series is an experimental reworking of GLK that will utilise new features of C++11 to improve the code-base and API.
Code is working but not rigorously tested. API is likely to change.
The "trunk" series represents the primary line of development rather than a stable release branch. This is sometimes also called MAIN or HEAD.
Switch GLK to C++11 ONLY. Remove all redundant features to focus on the core functionality.