add zen theme

lv_themes/lv_theme_zen.h

+/**
+ * @file lv_theme_zen.h
+ *
+ */
+
+#ifndef LV_THEME_ZEN_H
+#define LV_THEME_ZEN_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*********************
+ *      INCLUDES
+ *********************/
+#include "../../lv_conf.h"
+
+#if USE_LV_THEME_ZEN
+
+/*********************
+ *      DEFINES
+ *********************/
+
+/**********************
+ *      TYPEDEFS
+ **********************/
+
+/**********************
+ * GLOBAL PROTOTYPES
+ **********************/
+
+/**
+ * Initialize the zen theme
+ * @param hue [0..360] hue value from HSV color space to define the theme's base color
+ * @param font pointer to a font (NULL to use the default)
+ * @return pointer to the initialized theme
+ */
+lv_theme_t * lv_theme_zen_init(uint16_t hue, lv_font_t *font);
+
+/**
+ * Get a pointer to the theme
+ * @return pointer to the theme
+ */
+lv_theme_t * lv_theme_get_zen(void);
+
+/**********************
+ *      MACROS
+ **********************/
+
+#endif
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /*LV_THEME_ZEN_H*/