Merge add colors into constructor of gradient pattern. Since we also define color stops for gradient pattern and rear change it, mbe_pattern_add_color_stop_rgba() is merged into mb_pattern_create_radial() and mb_pattern_create_linear(). It also makes porting to graphic engines easier.

#ifndef __MBE_H_
#define __MBE_H_
#include <mb_config.h>

#ifdef CAIRO_GRAPH_ENGINE
#include <mb_graph_engine_cairo.h>
#endif

#ifdef SKIA_GRAPH_ENGINE
#include <mb_graph_engine_skia.h>
#endif

#endif /* __MBE_H_ */