TODO

- Handle GRL_RESOLVE_FULL when a certain key can be resolved by several plugins.
  -> Use alternative plugins if the selected one fails to resolve the key.
- Consider using GAsync callback interface for callback implementations.
  -> Also check issues for binding development related to this.
- Consider using the Ethos GObject plugin framework to replace our current
in-house plugin system.
- Multiple-plugin operations (i.e. search by text on all plugins).
- Python bindings
- Consider a more flexible post-processing mechanism for query
operations (browse, search, etc).
  -> We have to figure out if that's really necessary.
- Improve configuration interface
  -> Use strings for config keys