docs: Add effects chapter, with introduction and first recipe

Add an effects chapter which gives a broad overview of
the abstract classes in the effects API, plus a short
example of how to apply one of the stock Clutter
effects (ClutterColorizeEffect).

The recipe explains how to create a custom ClutterDeformEffect
to produce a page fold (code based on ClutterPageTurnEffect).

The example code includes the effect class plus a small
application to apply it to a texture.

doc/cookbook/examples/cb-page-fold-effect.h

@@ -0,0 +1,49 @@
+#ifndef __CB_PAGE_FOLD_EFFECT_H__
+#define __CB_PAGE_FOLD_EFFECT_H__
+
+#include <clutter/clutter.h>
+
+GType cb_page_fold_effect_get_type (void);
+
+#define CB_TYPE_PAGE_FOLD_EFFECT (cb_page_fold_effect_get_type ())
+#define CB_PAGE_FOLD_EFFECT(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), \
+                                                                         CB_TYPE_PAGE_FOLD_EFFECT, \
+                                                                         CbPageFoldEffect))
+#define CB_IS_PAGE_FOLD_EFFECT(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), \
+                                                                         CB_TYPE_PAGE_FOLD_EFFECT))
+#define CB_PAGE_FOLD_EFFECT_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), \
+                                                                      CB_TYPE_PAGE_FOLD_EFFECT, \
+                                                                      CbPageFoldEffectClass))
+#define CB_IS_PAGE_FOLD_EFFECT_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), \
+                                                                      CB_TYPE_PAGE_FOLD_EFFECT))
+#define CB_PAGE_FOLD_EFFECT_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), \
+                                                                        CB_TYPE_PAGE_FOLD_EFFECT, \
+                                                                        CbPageFoldEffectClass))
+
+typedef struct _CbPageFoldEffectPrivate CbPageFoldEffectPrivate;
+typedef struct _CbPageFoldEffect        CbPageFoldEffect;
+typedef struct _CbPageFoldEffectClass   CbPageFoldEffectClass;
+
+/* object */
+struct _CbPageFoldEffect
+{
+  ClutterDeformEffect      parent_instance;
+  CbPageFoldEffectPrivate *priv;
+};
+
+/* class */
+struct _CbPageFoldEffectClass
+{
+  ClutterDeformEffectClass parent_class;
+};
+
+ClutterEffect *cb_page_fold_effect_new (gdouble angle,
+                                        gdouble period);
+void cb_page_fold_effect_set_angle (CbPageFoldEffect *effect,
+                                    gdouble           angle);
+void cb_page_fold_effect_set_period (CbPageFoldEffect *effect,
+                                     gdouble           period);
+gdouble cb_page_fold_effect_get_period (CbPageFoldEffect *effect);
+gdouble cb_page_fold_effect_get_angle (CbPageFoldEffect *effect);
+
+#endif /* __CB_PAGE_FOLD_EFFECT_H__ */