* Immediately clear tags for invalidated regions without round-tripping
to the checker thread.
* Bump soname for ABI changes in 0.3
* Fix licenses to be LGPLv2.1+
* Add sysprof profiler marks for performance profiling
* Update example so people know to copy the button-press work
to update the menu immediately.
* Fix pkg-config fields
* Fix libspelling usage from subproject
* Make introspection building optional
* Documentation improvements
