Add animations (#15)

* animation: add xbm animations

* refactor: correct framebuffer terminology

* animation: add animations and effect

* animation: timing with TMOS scheduler

src/bmlist.c

@@ -0,0 +1,85 @@
+#include "bmlist.h"
+#include <memory.h>
+
+volatile static bm_t *current, *head, *tail;
+
+static void bm_add(bm_t *new, bm_t *prev, bm_t *next)
+{
+	next->prev = new;
+	new->next = next;
+	new->prev = prev;
+	prev->next = new;
+}
+
+bm_t *bmlist_insert(bm_t *at, bm_t *new) 
+{
+	bm_add(new, at, at->next);
+	return new;
+}
+
+bm_t *bmlist_append(bm_t *new) 
+{
+	bmlist_insert(tail, new);
+	tail = new;
+	return new;
+}
+
+bm_t *bmlist_gonext() 
+{
+	current = current->next;
+	current->anim_step = 0;
+	return current;
+}
+
+bm_t *bmlist_goprev() 
+{
+	current = current->prev;
+	current->anim_step = 0;
+	return current;
+}
+
+bm_t *bmlist_gohead()
+{
+	current = head;
+	current->anim_step = 0;
+	return current;
+}
+
+bm_t *bmlist_current()
+{
+	return current;
+}
+
+static void list_del(bm_t *prev, bm_t *next)
+{
+	prev->next = next;
+	next->prev = prev;
+}
+
+bm_t *bmlist_drop(bm_t *bm)
+{
+	list_del(bm->prev, bm->next);
+	return bm->next;
+}
+
+bm_t *bm_new(uint16_t width)
+{
+	bm_t *bm = malloc(sizeof(bm_t));
+	memset(bm, 0, sizeof(bm_t));
+
+	bm->width = width;
+	bm->buf = malloc(width * sizeof(uint16_t));
+	memset(bm->buf, 0, width * sizeof(uint16_t));
+
+	bm->next = bm;
+	bm->prev = bm;
+
+	return bm;
+}
+
+void bmlist_init(uint16_t first_bm_width)
+{
+	current = bm_new(first_bm_width);
+	head = current;
+	tail = current;
+}