Implement row annotations for DeeModel

[Mikkel Kamstrup Erlandsen]

It's a common pattern that model consumers needs to map each individual row to some internal data structure or value (fx. a widget). Currently this can only be achieved by maintaining a map of row iters to the data members which must then be kept in sync with the model.

I propose we add a "Model Annotation API" ala:

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typedef guint DeeModelAnnotation;

/**
 * dee_model_register_annotation:
 * @destroy: Callback to free annotation set on the model with
 * dee_model_set_annotation(). Called when the row is
 * removed, the annotation is cleared, or the model is
 * finalized.
 *
 * Create a new annotation.
 *
 * Returns: A new annotation key that can be used to get and
 * set annotation values
 */
DeeModelAnnotation dee_model_register_annotation (GDestroyNotify destroy);

void dee_model_set_annotation (DeeModel *model,
                               DeeModelIter *row,
                               DeeModelAnnotation anno,
                               gpointer anno_value);

gpointer dee_model_get_annotation (DeeModel *model,
                                   DeeModelIter *row,
                                   DeeModelAnnotation anno);

void dee_model_clear_annotation (DeeModel *model,
                                 DeeModelIter *row,
                                 DeeModelAnnotation anno);

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[Mark Shuttleworth (sabdfl)]

Very neatly defined, Mikkel.

[Mikkel Kamstrup Erlandsen (kamstrup)]

The API is merged and looks like:

DeeModelTag* dee_model_register_annotation (DeeModel *model, GDestroyNotify destroy);

void dee_model_set_tag (DeeModel *model,
                               DeeModelIter *row,
                               DeeModelTag *tag,
                               gpointer value);

gpointer dee_model_get_tag (DeeModel *model,
                                   DeeModelIter *row,
                                   DeeModelTag *tag);

void dee_model_clear_tag (DeeModel *model,
                                 DeeModelIter *row,
                                 DeeModelTag *tag);